Light-emitting element and electronic device

ABSTRACT

An object is to provide a light-emitting element with high emission efficiency which includes a novel carbazole derivative that has a wide energy gap and can be used for a transport layer or a host material in a light-emitting element. A carbazole derivative in which the 4-position of dibenzothiophene or dibenzofuran is bonded to the 2- or 3-position of carbazole has been able to be provided by use of the carbazole derivative. Further, a light-emitting element having high emission efficiency has been able to be provided by use of the carbazole derivative.

TECHNICAL FIELD

The present invention relates to a light-emitting element and anelectronic device each using a carbazole derivative. The presentinvention further relates to the carbazole derivative and alight-emitting material and a light-emitting element material each usingthe carbazole derivative.

BACKGROUND ART

A display device using a light-emitting element (organic EL element) inwhich an organic compound is used as a light-emitting substance has beendeveloped rapidly as a next generation lighting device or display devicebecause it has advantages that such a light-emitting element can bemanufactured to be thin and lightweight, has very high response speed,and has low power consumption.

In an organic EL element, when a voltage is applied between a pair ofelectrodes between which a light-emitting layer is interposed, electronsand holes are injected from the electrodes. The injected electrons andholes are recombined to form an excited state of a light-emittingsubstance contained in the light-emitting layer, and when the excitedstate relaxes to a ground state, light is emitted. A wavelength of lightemitted from a light-emitting substance is peculiar to thelight-emitting substance; thus, by using different types of organiccompounds as light-emitting substances, light-emitting elements whichexhibit various wavelengths, i.e., various colors can be obtained.

In a case of a display device which is expected to display images, suchas a display, at least three colors of light, i.e., red, green, and blueare required to be obtained in order to reproduce full-color images. Inthe case of a lighting device, in order to obtain high color renderingproperty, light having wavelength components thoroughly in the visiblelight region is ideally obtained. Actually, two or more kinds of lighthaving different wavelengths are mixed to be used for lightingapplication in many cases. Note that it is known that by mixing light ofthree colors, red, green, and blue, white light emission having highcolor rendering property can be obtained.

Light emitted from a light-emitting substance is peculiar to thesubstance as described above. However, important performances as alight-emitting element, such as lifetime or power consumption, are notonly dependent on a light-emitting substance but also greatly dependenton layers other than a light-emitting layer, an element structure,properties of the light-emitting substance and a host, compatibilitybetween them, or the like. Therefore, it is true that many kinds ofmaterials are necessary for light-emitting elements in order to show thegrowth of this field. For the above-described reasons, materials forlight-emitting elements which have a variety of molecular structureshave been proposed (for example, see Patent Document 1).

REFERENCE Patent Document

-   [Patent Document 1] Japanese. Published Patent Application No.    2007-15933

DISCLOSURE OF INVENTION

Now there is a problem with light-emitting elements under currentdevelopment: light-emitting elements that emit blue light have poorercharacteristics than light-emitting elements that emit red to greenlight. This is due to the fact that a light-emitting substance having awide energy gap is needed to emit blue light, and a further wider energygap is needed for a substance used for a host for dispersion of thelight-emitting substance in a light-emitting layer or a substance usedfor a transport layer adjacent to a light-emitting region containing thelight-emitting substance

If a material whose energy gap is not wide enough is used as a hostmaterial or a material for a layer adjacent to a light-emitting region,exciton energy is transferred to the material; thus, there occurs aproblem such as reduction in the emission efficiency and color purity ofthe light-emitting element.

Therefore, an object of one embodiment of the present invention is toprovide a novel carbazole derivative that has a wide energy gap and canbe used for a transport layer or a host material in a light-emittingelement or to provide a light-emitting element with high emissionefficiency which includes the carbazole derivative.

Another object of one embodiment of the present invention is to providea light-emitting element driven with a low driving voltage in which theabove novel carbazole derivative is used.

Another object of one embodiment of the present invention is to providea light-emitting element having a long lifetime in which the above novelcarbazole derivative is used.

Note that in one embodiment of the present invention, it is onlynecessary that at least one of the above-described objects is achieved.

The present inventors have been able to synthesize a carbazolederivative in which the 4-position of dibenzothiophene or dibenzofuranis bonded to the 2- or 3-position of carbazole, as a substance having awide band gap and a moderate carrier-transport property which can besuitably used as a material of a light-emitting element. Further, alight-emitting element having high emission efficiency has been able tobe provided by use of the carbazole derivative. Furthermore, alight-emitting element driven with a low driving voltage has been ableto be provided by use of the carbazole derivative. Further, alight-emitting element having a long lifetime has also been able to beprovided by use of the carbazole derivative.

Specifically, one embodiment of the present invention is alight-emitting element including a layer containing an organic compoundbetween a pair of electrodes, in which the layer containing an organiccompound contains a material having an N-carbazolyl group in which the4-position of a dibenzothiophene skeleton or of a dibenzofuran skeletonis bonded to the 2- or 3-position of carbazole.

Another embodiment of the present invention is a light-emitting elementincluding a layer containing an organic compound between a pair ofelectrodes, in which the layer containing an organic compound contains amaterial having an N-carbazolyl group in which the 4-position of adibenzothiophene skeleton or of a dibenzofuran skeleton is bonded to the2- or 3-position of and 6- or 7-position of carbazole.

Another embodiment of the present invention is a light-emitting elementincluding a layer containing an organic compound between a pair ofelectrodes, in which the layer containing an organic compound contains amaterial having an N-carbazolyl group in which the 4-position of adibenzothiophene skeleton or of a dibenzofuran skeleton is bonded to the2- and 7-positions of or 3- and 6-positions of carbazole.

Another embodiment of the present invention is a light-emitting elementincluding a layer containing an organic compound between a pair ofelectrodes, in which the layer containing an organic compound contains acarbazole derivative represented by the following general formula (G1).

In the formula, Ar represents an aryl group having 6 to 70 carbon atomsor a heteroaromatic group having 1 to 70 carbon atoms. In addition, R⁰represents a group represented by the following general formula (g1),and R⁸ represents any one of hydrogen, an alkyl group having 1 to 6carbon atoms, an aryl group having 6 to 15 carbon atoms, and a grouprepresented by the following general formula (g2). Note that thesubstitution site of R⁰ is a carbon atom represented by either α or β,and the substitution site of R⁸ is a carbon atom represented by either δor δ.

(In the formula, X¹ represents oxygen or sulfur, and R¹ to R⁷individually represent any one of hydrogen, an alkyl group having 1 to 6carbon atoms, and an aryl group having 6 to 15 carbon atoms.)

(In the formula, X² represents oxygen or sulfur, and R⁹ to R¹⁵individually represent any one of hydrogen, an aryl group having 6 to 15carbon atoms, and an alkyl group having 1 to 6 carbon atoms.)

Another embodiment of the present invention is a light-emitting elementhaving any of the above structures, in which R⁰ is bonded to theposition of α when a substituent R⁸ represented by the general formula(g2) is bonded to the position of γ, or R⁰ is bonded to the position ofβ when the substituent R⁸ is bonded to the position of δ.

Another embodiment of the present invention is a light-emitting elementincluding a layer containing an organic compound between a pair ofelectrodes, in which the layer containing an organic compound contains acarbazole derivative represented by the following general formula (G1).

In the formula, Ar represents an aryl group having 6 to 70 carbon atomsor a heteroaromatic group having 1 to 70 carbon atoms. In addition, R⁰represents a group represented by the following general formula (g3),and R⁸ represents any one of hydrogen, an aryl group having 6 to 15carbon atoms, an alkyl group having 1 to 6 carbon atoms, and a grouprepresented by the following general formula (g4). Note that thesubstitution site of R⁰ is a carbon atom represented by either α or β,and the substitution site of R⁸ is a carbon atom represented by either γor δ.

In the formula, X¹ represents oxygen or sulfur, and R¹, R³, and R⁶individually represent any one of hydrogen, an aryl group having 6 to 15carbon atoms, and an alkyl group having 1 to 6 carbon atoms.

Note that in the formula, X² represents oxygen or sulfur, and R⁹, R¹¹,and R¹⁴ individually represent any one of hydrogen, an aryl group having6 to 15 carbon atoms, and an alkyl group having 1 to 6 carbon atoms.

Another embodiment of the present invention is a light-emitting elementincluding a layer containing an organic compound between a pair ofelectrodes, in which the layer containing an organic compound contains acarbazole derivative represented by the following general formula (G1).

In the formula, Ar represents an aryl group having 6 to 70 carbon atomsor a heteroaromatic group having 1 to 70 carbon atoms. Further, R⁰represents a group represented by the following general formula (g3),and R⁸ represents any of hydrogen and a group represented by thefollowing general formula (g4). Note that the substitution site of R⁰ isa carbon atom represented by either α or β, and the substitution site ofR⁸ is a carbon atom represented by either γ or δ.

In the formula, X¹ represents oxygen or sulfur, and R¹, R³, and R⁶individually represent any one of hydrogen, an aryl group having 6 to 15carbon atoms, and an alkyl group having 1 to 6 carbon atoms.

Note that in the formula, X² represents oxygen or sulfur, and R⁹, R¹¹,and R¹⁴ individually represent any one of hydrogen, an aryl group having6 to 15 carbon atoms, and an alkyl group having 1 to 6 carbon atoms.

Another embodiment of the present invention is a light-emitting elementhaving any of the above structures; in which R⁰ is bonded to theposition of α when a substituent R⁸ represented by the general formula(g4) is bonded to the position of γ, or R⁰ is bonded to the position ofβ when the substituent R⁸ is bonded to the position of δ.

Another embodiment of the present invention is a light-emitting elementincluding a layer containing an organic compound between a pair ofelectrodes, in which the layer containing an organic compound contains acarbazole derivative represented by the following general formula (G3).

In the formula, Ar represents an aryl group having 6 to 70 carbon atomsor a heteroaromatic group having 1 to 70 carbon atoms. Further, R⁰represents a group represented by the following general formula (g5),and R⁸ represents any of hydrogen and a group represented by thefollowing general formula (g6).

In the formula, X¹ represents oxygen or sulfur.

In the formula, X² represents oxygen or sulfur.

Another embodiment of the present invention is a light-emitting elementhaving any of the above structures, in which R⁰ is bonded to theposition of α when a substituent R⁸ represented by the general formula(g6) is bonded to the position of γ, or R⁰ is bonded to the position ofβ when the substituent R⁸ is bonded to the position of δ.

Another embodiment of the present invention is a light-emitting elementincluding a layer containing an organic compound between a pair ofelectrodes, in which the layer containing an organic compound contains acarbazole derivative represented by the following general formula (G4).

Note that, in the formula, X represents oxygen or sulfur and Arrepresents an aryl group having 6 to 70 carbon atoms or a heteroaromaticgroup having 1 to 70 carbon atoms.

Another embodiment of the present invention is a light-emitting elementincluding a layer containing an organic compound between a pair ofelectrodes, in which the layer containing an organic compound contains acarbazole derivative represented by the following general formula (G5).

Note that, in the formula, X¹ and X² individually represent oxygen orsulfur and Ar represents an aryl group having 6 to 70 carbon atoms or aheteroaromatic group having 1 to 70 carbon atoms.

Another embodiment of the present invention is a light-emitting elementincluding a layer containing an organic compound between a pair ofelectrodes, in which the layer containing an organic compound contains acarbazole derivative represented by the following general formula (G6).

Note that, in the formula, X¹ and X² individually represent oxygen orsulfur and Ar represents an aryl group having 6 to 70 carbon atoms or aheteroaromatic group having 1 to 70 carbon atoms.

A carbazole derivative having any of the above-described structures is alight-emitting element material having a wide energy gap, and can beused for a transport layer or as a host material in the light-emittingelement. A light-emitting element using the carbazole derivative can bea light-emitting element having high emission efficiency. In addition, alight-emitting element using the carbazole derivative can be alight-emitting element driven with a low driving voltage. Further, alight-emitting element using the carbazole derivative can be alight-emitting element having a long lifetime.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are conceptual diagrams of light-emitting elements.

FIGS. 2A and 2B are conceptual diagrams of an active matrixlight-emitting device.

FIGS. 3A and 3B are conceptual diagrams of a passive matrixlight-emitting device.

FIGS. 4A to 4D each illustrate an electronic device.

FIG. 5 illustrates an electronic device.

FIG. 6 illustrates a lighting device.

FIG. 7 illustrates lighting devices.

FIG. 8 shows luminance versus current density characteristics of alight-emitting element 1 and a light-emitting element 2.

FIG. 9 shows luminance versus voltage characteristics of thelight-emitting element 1 and the light-emitting element 2.

FIG. 10 shows current efficiency versus luminance characteristics of thelight-emitting element 1 and the light-emitting element 2.

FIG. 11 shows emission spectra of the light-emitting element 1 and thelight-emitting element 2.

FIG. 12 shows normalized luminance versus time characteristics of thelight-emitting element 1 and the light-emitting element 2.

FIG. 13 shows luminance versus current density characteristics of alight-emitting element 3 and a light-emitting element 4.

FIG. 14 shows luminance versus voltage characteristics of thelight-emitting element 3 and the light-emitting element 4.

FIG. 15 shows current efficiency versus luminance characteristics of thelight-emitting element 3 and the light-emitting element 4.

FIG. 16 shows emission spectra of the light-emitting element 3 and thelight-emitting element 4.

FIG. 17 shows normalized luminance versus time characteristics of thelight-emitting element 3 and the light-emitting element 4.

FIG. 18 shows luminance versus current density characteristics of alight-emitting element 5 and a light-emitting element 6.

FIG. 19 shows luminance versus voltage characteristics of thelight-emitting element 5 and the light-emitting element 6.

FIG. 20 shows current efficiency versus luminance characteristics of thelight-emitting element 5 and the light-emitting element 6.

FIG. 21 shows emission spectra of the light-emitting element 5 and thelight-emitting element 6.

FIG. 22 shows normalized luminance versus time characteristics of thelight-emitting element 5 and the light-emitting element 6.

FIG. 23 shows luminance versus current density characteristics of alight-emitting element 7.

FIG. 24 shows luminance versus voltage characteristics of thelight-emitting element 7.

FIG. 25 shows current efficiency versus luminance characteristics of thelight-emitting element 7.

FIG. 26 shows an emission spectrum of the light-emitting element 7.

FIG. 27 shows luminance versus current density characteristics of alight-emitting element 8.

FIG. 28 shows luminance versus voltage characteristics of thelight-emitting element 8.

FIG. 29 shows current efficiency versus luminance characteristics of thelight-emitting element 8.

FIG. 30 shows an emission spectrum of the light-emitting element 8.

FIGS. 31A and 31B are ¹H NMR charts of DBTCzBIm-II.

FIG. 32 shows an absorption spectrum of DBTCzBIm-II in a solution ofDBTCzBIm-II (the solvent of which is toluene).

FIG. 33 shows an absorption spectrum of DBTCzBIm-II in a thin filmstate.

FIG. 34 shows an emission spectrum of DBTCzBIm-II in the solution ofDBTCzBIm-II (the solvent of which is toluene).

FIG. 35 shows an emission spectrum of DBTCzBIm-II in a thin film state.

FIGS. 36A and 36B are ¹H NMR charts of DBFCzBIm-II.

FIG. 37 shows an absorption spectrum of DBFCzBIm-II in a solution ofDBFCzBIm-II (the solvent of which is toluene).

FIG. 38 shows an absorption spectrum of DBFCzBIm-II in a thin filmstate.

FIG. 39 shows an emission spectrum of DBFCzBIm-II in the solution ofDBFCzBIm-II (the solvent of which is toluene).

FIG. 40 shows an emission spectrum of DBFCzBIm-II in a thin film state.

FIGS. 41A and 41B are ¹H NMR charts of DBTCzTp-II.

FIG. 42 shows an absorption spectrum of DBTCzTp-II in a solution ofDBTCzTp-II (the solvent of which is toluene).

FIG. 43 shows an absorption spectrum of DBTCzTp-II in a thin film state.

FIG. 44 shows an emission spectrum of DBTCzTp-II in the solution ofDBTCzTp-II (the solvent of which is toluene).

FIG. 45 shows an emission spectrum of DBTCzTp-II in a thin film state.

FIGS. 46A and 46B are ¹H NMR charts of DBFCzTp-II.

FIG. 47 shows an absorption spectrum of DBFCzTp-II in a solution ofDBFCzTp-II (the solvent of which is toluene).

FIG. 48 shows an absorption spectrum of DBFCzTp-II in a thin film state.

FIG. 49 shows an emission spectrum of DBFCzTp-II in the solution ofDBFCzTp-II (the solvent of which is toluene).

FIG. 50 shows an emission spectrum of DBFCzTp-II in a thin film state.

FIG. 51 is a ¹H NMR chart of DBTCzPA-II.

FIG. 52 shows an absorption spectrum of DBTCzPA-II in a solution ofDBTCzPA-II (the solvent of which is toluene).

FIG. 53 shows an absorption spectrum of DBTCzPA-II in a thin film state.

FIG. 54 shows an emission spectrum of DBTCzPA-II in the solution ofDBTCzPA-II (the solvent of which is toluene).

FIG. 55 shows an emission spectrum of DBTCzPA-II in a thin film state.

FIG. 56 is a ¹H NMR chart of DBFCzPA-II.

FIG. 57 shows an absorption spectrum of DBFCzPA-II in a solution ofDBFCzPA-II (the solvent of which is toluene).

FIG. 58 shows an absorption spectrum of DBFCzPA-II in a thin film state.

FIG. 59 shows an emission spectrum of DBFCzPA-II in the solution ofDBFCzPA-II (the solvent of which is toluene).

FIG. 60 shows an emission spectrum of DBFCzPA-II in a thin film state.

FIGS. 61A and 61B are ¹H NMR charts of DBT2PC-II.

FIG. 62 shows an absorption spectrum of DBT2PC-II in a solution ofDBT2PC-II (the solvent of which is toluene).

FIG. 63 shows an absorption spectrum of DBT2PC-II in a thin film state.

FIG. 64 shows an emission spectrum of DBT2PC-II in the solution ofDBT2PC-II (the solvent of which is toluene).

FIG. 65 shows an emission spectrum of DBT2PC-II in a thin film state.

FIGS. 66A and 66B are ¹H NMR charts of 2,7DBT2PC-II.

FIG. 67 shows an absorption spectrum of 2,7DBT2PC-II in a solution of2,7DBT2PC-II (the solvent of which is toluene).

FIG. 68 shows an absorption spectrum of 2,7DBT2PC-II in a thin filmstate.

FIG. 69 shows an emission spectrum of 2,7DBT2PC-II in the solution of2,7DBT2PC-II (the solvent of which is toluene).

FIG. 70 shows an emission spectrum of 2,7DBT2PC-II in a thin film state.

FIGS. 71A and 71B are NMR charts of DBF2PC-II.

FIGS. 72A and 72B show an absorption and emission spectra of DBF2PC-II.

FIG. 73 shows luminance versus voltage characteristics of alight-emitting element 9.

FIG. 74 shows current efficiency versus luminance characteristics of thelight-emitting element 9.

FIG. 75 shows current versus voltage characteristics of thelight-emitting element 9.

FIG. 76 shows power efficiency versus luminance characteristics of thelight-emitting element 9.

FIG. 77 shows external quantum efficiency-luminance characteristics ofthe light-emitting element 9.

FIG. 78 shows an emission spectrum of the light-emitting element 9.

FIG. 79 shows normalized luminance versus time characteristics of thelight-emitting element 9.

FIGS. 80A and 80B are NMR charts of mDBTCz2P-II.

FIGS. 81A and 81B show an absorption and emission spectra ofmDBTCz2P-II.

FIG. 82 shows luminance versus current density characteristics oflight-emitting element 10.

FIG. 83 shows luminance versus voltage characteristics of alight-emitting element 10.

FIG. 84 shows current efficiency versus luminance characteristics of thelight-emitting element 10.

FIG. 85 shows current versus voltage characteristics of thelight-emitting element 10.

FIG. 86 shows an emission spectrum of the light-emitting element 10.

FIG. 87 shows normalized luminance versus time characteristics of thelight-emitting element 10.

FIG. 88 shows luminance versus current density characteristics oflight-emitting element 11.

FIG. 89 shows luminance versus voltage characteristics of alight-emitting element 11.

FIG. 90 shows current efficiency versus luminance characteristics of thelight-emitting element 11.

FIG. 91 shows current versus voltage characteristics of thelight-emitting element 11.

FIG. 92 shows luminance versus current density characteristics of alight-emitting element 12.

FIG. 93 shows luminance versus voltage characteristics of thelight-emitting element 12.

FIG. 94 shows current efficiency versus luminance characteristics of thelight-emitting element 12.

FIG. 95 shows current versus voltage characteristics of thelight-emitting element 12.

FIG. 96 shows an emission spectrum of the light-emitting element 11.

FIG. 97 shows an emission spectrum of the light-emitting element 12.

FIG. 98 shows normalized luminance versus time characteristics of thelight-emitting element 11.

FIG. 99 shows normalized luminance versus time characteristics of thelight-emitting element 12.

FIGS. 100A and 100B are NMR charts of mDBTCzPA-II.

FIGS. 101A and 101B show an absorption and emission spectra ofmDBTCzPA-II.

FIG. 102 shows luminance versus current density characteristics of alight-emitting element 13.

FIG. 103 shows luminance versus voltage characteristics of thelight-emitting element 13.

FIG. 104 shows current efficiency versus luminance characteristics ofthe light-emitting element 13.

FIG. 105 shows current versus voltage characteristics of thelight-emitting element 13.

FIG. 106 shows an emission spectrum of the light-emitting element 13.

FIG. 107 shows normalized luminance versus time characteristics of thelight-emitting element 13.

FIGS. 108A and 108B are NMR charts of mDBFCzPA-II.

FIGS. 109A and 109B show an absorption and emission spectra ofmDBFCzPA-II.

FIG. 110 shows luminance versus current density characteristics of alight-emitting element 14.

FIG. 111 shows luminance versus voltage characteristics of thelight-emitting element 14.

FIG. 112 shows current efficiency versus luminance characteristics ofthe light-emitting element 14.

FIG. 113 shows current versus voltage characteristics of thelight-emitting element 14.

FIG. 114 shows an emission spectrum of the light-emitting element 14.

FIG. 115 shows normalized luminance versus time characteristics of thelight-emitting element 14.

FIGS. 116A and 116B are NMR charts of DBTCzPA-IV.

FIGS. 117A and 117B show an absorption and emission spectra ofDBTCzPA-IV.

FIG. 118 shows luminance versus current density characteristics of alight-emitting element 15.

FIG. 119 shows luminance versus voltage characteristics of thelight-emitting element 15.

FIG. 120 shows current efficiency versus luminance characteristics ofthe light-emitting element 15.

FIG. 121 shows current versus voltage characteristics of thelight-emitting element 15.

FIG. 122 shows an emission spectrum of the light-emitting element 15.

FIG. 123 shows normalized luminance versus time characteristics of thelight-emitting element 15.

FIGS. 124A and 124B are NMR charts of 2DBTCzPPA-II.

FIGS. 125A and 125B show an absorption and emission spectra of2DBTCzPPA-II.

FIG. 126 shows luminance versus current density characteristics of alight-emitting element 16.

FIG. 127 shows luminance versus voltage characteristics of thelight-emitting element 16.

FIG. 128 shows current efficiency versus luminance characteristics ofthe light-emitting element 16.

FIG. 129 shows current versus voltage characteristics of thelight-emitting element 16.

FIG. 130 shows an emission spectrum of the light-emitting element 16.

FIG. 131 shows normalized luminance versus time characteristics of thelight-emitting element 16.

FIGS. 132A and 132B are NMR charts of 2DBFCzPPA-II.

FIGS. 133A and 133B show an absorption and emission spectra of2DBFCzPPA-II.

FIG. 134 shows luminance versus current density characteristics of alight-emitting element 17.

FIG. 135 shows luminance versus voltage characteristics of thelight-emitting element 17.

FIG. 136 shows current efficiency versus luminance characteristics ofthe light-emitting element 17.

FIG. 137 shows current versus voltage characteristics of thelight-emitting element 17.

FIG. 138 shows an emission spectrum of the light-emitting element 17.

FIG. 139 shows normalized luminance versus time characteristics of thelight-emitting element 17.

FIGS. 140A and 140B are NMR charts of 2mDBTCzPPA-II.

FIGS. 141A and 141B show an absorption and emission spectra of2mDBTCzPPA-II.

FIG. 142 shows luminance versus current density characteristics of alight-emitting element 18.

FIG. 143 shows luminance versus voltage characteristics of thelight-emitting element 18.

FIG. 144 shows current efficiency versus luminance characteristics ofthe light-emitting element 18.

FIG. 145 shows current versus voltage characteristics of thelight-emitting element 18.

FIG. 146 shows an emission spectrum of the light-emitting element 18.

FIG. 147 shows normalized luminance versus time characteristics of thelight-emitting element 18.

FIGS. 148 A and 148 B are NMR charts of 2mDBFCzPPA-II.

FIGS. 149A and 149B show an absorption and emission spectra of2mDBFCzPPA-II.

FIG. 150 shows luminance versus current density characteristics of alight-emitting element 19.

FIG. 151 shows luminance versus voltage characteristics of thelight-emitting element 19.

FIG. 152 shows current efficiency versus luminance characteristics ofthe light-emitting element 19.

FIG. 153 shows current versus voltage characteristics of thelight-emitting element 19.

FIG. 154 shows an emission spectrum of the light-emitting element 19.

FIG. 155 shows normalized luminance versus time characteristics of thelight-emitting element 19.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention are described. It iseasily understood by those skilled in the art that modes and detailsdisclosed herein can be modified in various ways without departing fromthe spirit and the scope of the present invention. Therefore, thepresent invention is not construed as being limited to description ofthe embodiments.

Embodiment 1

A light-emitting element in this embodiment is a light-emitting elementincluding a substance having an N-carbazolyl group whose carbon atom atthe 2- or 3-position of carbazole is bonded to the 4-position of adibenzothiophene skeleton or the 4-position of a dibenzofuran skeleton.Note that the dibenzothiophene skeleton or dibenzofuran skeleton and thecarbazole skeleton may or may not have a substituent.

In the case where the dibenzothiophene or dibenzofuran bonded to theN-carbazolyl group has a substituent, as the substituent, any of an arylgroup having 6 to 15 carbon atoms and an alkyl group having 1 to 6carbon atoms can be given.

In the case where the carbazole in the N-carbazolyl group has anothersubstituent, the substitution site of the substituent is the 6- or7-position of the carbazole, and the substituent can be any of an arylgroup having 6 to 15 carbon atoms, an alkyl group having 1 to 6 carbonatoms, a dibenzothiophen-4-yl group, and a dibenzofuran-4-yl group. Inthe case where the dibenzothiophen-4-yl group or the dibenzofuran-4-ylgroup is selected as the substituent that is bonded to the 6- or7-position of the carbazole, the dibenzothiophen-4-yl group or thedibenzofuran-4-yl group may further have a substituent that can beselected from an aryl group having 6 to 15 carbon atoms and an alkylgroup having 1 to 6 carbon atoms. For easier synthesis, thedibenzothiophen-4-yl group or the dibenzofuran-4-yl group is preferablysubstituted at the 7-position of the carbazole when thedibenzothiophen-4-yl group or the dibenzofuran-4-yl group is selected asthe substituent that is bonded to the 6- or 7-position of the carbazoleand the dibenzothiophene or the dibenzofuran is bonded to the 2-positionof the carbazole, and the dibenzothiophen-4-yl group or thedibenzofuran-4-yl group is preferably substituted at the 6-position ofthe carbazole when the dibenzothiophene or the dibenzofuran is bonded tothe 3-position of the carbazole. Note that the dibenzothiophene ordibenzofuran which is bonded to the 2- or 3-position of the carbazoleand the substituent bonded to the 6- or 7-position of the carbazole arepreferably of the same type for easier synthesis.

By introduction of such an N-carbazolyl group, a hole-injection andhole-transport properties can be imparted to a substance into which theN-carbazolyl group is introduced without involving a reduction in bandgap or triplet excitation energy: that is, a material for alight-emitting element having a wide band gap or high triplet excitationenergy and an excellent carrier-transport property can be provided.Owing to the wide band gap or high triplet excitation energy, the lossof excitation energy is small in a light-emitting element including sucha material, and accordingly, the light-emitting element can have highemission efficiency. In addition, a light-emitting element driven with alow driving voltage can be obtained owing to the excellent carriermobility.

The above-described N-carbazolyl derivative has a rigid group such asdibenzothiophene or dibenzofuran, and thus the morphology is excellentand the film quality is stable. Further, the thermophysical property isalso excellent. From the above, a light-emitting element that uses asubstance having such an N-carbazolyl derivative can be a light-emittingelement having a long lifetime.

Note that with the above-described N-carbazolyl group used byintroduction into a substance that has an electron-transport property, amaterial having both the electron-transport property and ahole-transport property, i.e., a bipolar material, can be obtained. Withthe use of the bipolar material for a light-emitting layer in alight-emitting element, localization of an emission region can beprevented, concentration quenching or triplet-triplet annihilation (T-Tannihilation) can be suppressed, and a light-emitting element havinghigh emission efficiency can be obtained.

A substance having any of the above-described N-carbazolyl groups canalso be represented by the following general formula (G1).

In the formula (G1), Ar may be any group, but, in consideration of theuse for the light-emitting element, it is preferably an aryl grouphaving 6 to 70 carbon atoms or a heteroaromatic group having 1 to 70carbon atoms. When Ar is such a group, the light-emitting element can befabricated by use of a usual method, such as an evaporation method or awet process, in the fabrication of the light-emitting element. Note thata structure in which the molecular weight of the carbazole derivative is1200 or less is further preferred for easier evaporation.

R⁰ represents a group represented by the following general formula (g1).Note that the substitution site of R⁰ is a carbon atom represented byeither α or β.

In the formula (g1), X¹ represents oxygen or sulfur, and R¹ to R⁷individually represent any one of hydrogen, an alkyl group having 1 to 6carbon atoms, and an aryl group having 6 to 15 carbon atoms.

A carbazole derivative having the above-described structure has a wideband gap or high triplet excitation energy, and a light-emitting elementusing the carbazole derivative can be a light-emitting element havinghigh emission efficiency. Further, such a carbazole derivative has anexcellent carrier-transport property, and a light-emitting element usingthe carbazole derivative can be a light-emitting element driven with alow driving voltage. In addition, the above-described carbazolederivative has a rigid group such as dibenzothiophene or dibenzofuran,and thus the morphology is excellent and the film quality is stable.Further, the thermophysical property is also excellent. From the above,the above carbazole derivative can realize a light-emitting elementhaving a long lifetime.

Note that the carbazole derivative represented by the above generalformula (G1) may have a substituent represented by R⁸, as alsoillustrated in the above general formula (G1). R⁸ represents any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, an aryl grouphaving 6 to 15 carbon atoms, and a group represented by the followinggeneral formula (g2). Note that the substitution site of R⁸ is a carbonatom represented by either γ or δ.

In the formula (g2), X² represents oxygen or sulfur, and R⁹ to R¹⁵individually represent any one of hydrogen, an aryl group having 6 to 15carbon atoms, and an alkyl group having 1 to 6 carbon atoms.

In the case where R⁸ is a substituent represented by the above generalformula (g2), for easier synthesis, it is preferable that thesubstitution site of R⁸ be γ when the substitution site of thesubstituent represented by the above general formula (g1) is α, or thatthe substitution site of R⁸ be δ when the substitution site of thesubstituent represented by the above general formula (g1) is β. Further,in the case where R⁸ is a substituent other than hydrogen, R⁸ ispreferably the same group as the above general formula (g1) for easiersynthesis.

In the case where the group represented by the above general formula(g1) further includes a substituent, the substitution site of thesubstituent is preferably a site represented by R¹, R³, or R⁶ for amaterial cost reduction owing to availability of the material and toeasiness of the synthesis. From the same point of view, it is furtherpreferable that R¹ to R⁷ be all hydrogen.

Also in the case where the group represented by (g2) is used as R⁸, thesubstitution site of the substituent is preferably a site represented byR⁹, R¹¹, or R¹⁴, and further preferably, R⁹ to R¹⁵ are all hydrogen.

Examples of Ar in the formula are the groups represented by thefollowing structural formulae (Ar-1) to (Ar-7), but no limitation isintended thereto as described above.

A carbazole derivative having the above-described structure has a wideband gap or high triplet excitation energy and enables efficientemission of even fluorescence or phosphorescence with high energy;therefore, such a carbazole derivative can be suitably used for alight-emitting element for emitting blue fluorescence or greenphosphorescence, so that light-emitting element can be a light-emittingelement having high emission efficiency. In addition, the carbazolederivative is suitable as a carrier-transport material as well owing tothe excellent carrier-transport property, and thus a light-emittingelement driven with a low driving voltage can also be provided. Thecarbazole derivative of this embodiment has a rigid group such asdibenzothiophene or dibenzofuran, and thus the morphology is excellentand the film quality is stable. Further, the thermophysical property isalso excellent. From the above, a light-emitting element that uses sucha carbazole derivative can be a light-emitting element having a longlifetime.

One embodiment of a light-emitting element using any of the carbazolederivatives is described with reference to FIG. 1A.

A light-emitting element of this embodiment includes a plurality oflayers between a pair of electrodes. In this embodiment, thelight-emitting element includes a first electrode 102, a secondelectrode 104, and an EL layer 103 provided between the first electrode102 and the second electrode 104. In addition, in this embodiment, thefirst electrode 102 functions as an anode and the second electrode 104functions as a cathode. In other words, when a voltage is appliedbetween the first electrode 102 and the second electrode 104 such thatthe potential of the first electrode 102 is higher than that of thesecond electrode 104, light emission can be obtained.

The substrate 101 is used as a support of the light-emitting element. Asthe substrate 101, glass, plastic or the like can be used, for example.Note that a material other than glass or plastic can be used as far asit can function as a support of a light-emitting element.

The first electrode 102 is preferably formed using a metal, an alloy, aconductive compound, a mixture of them, or the like having a high workfunction (specifically, a work function of 4.0 eV or higher).Specifically, for example, indium oxide-tin oxide (ITO: indium tinoxide), indium oxide-tin oxide containing silicon or silicon oxide,indium oxide-zinc oxide (IZO: indium zinc oxide), indium oxidecontaining tungsten oxide and zinc oxide (IWZO), and the like can begiven. Films of these conductive metal oxides are usually formed bysputtering; however, a sol-gel method or the like may also be used. Forexample, indium zinc oxide (IZO) can be formed by a sputtering methodusing a target in which zinc oxide is added to indium oxide at 1 wt % to20 wt %. Moreover, indium oxide containing tungsten oxide and zinc oxide(IWZO) can be formed by a sputtering method using a target in whichtungsten oxide is added to indium oxide at 0.5 wt % to 5 wt % and zincoxide is added to indium oxide at 0.1 wt % to 1 wt %. Besides, gold(Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr),molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd),graphene, nitride of a metal material (e.g., titanium nitride), and thelike can be given.

There is no particular limitation on a stacked structure of the EL layer103. The EL layer 103 may be formed as appropriate by combining a layerthat contains a substance having a high electron-transport property, alayer that contains a substance having a high hole-transport property, alayer that contains a substance having a high electron-injectionproperty, a layer that contains a substance having a high hole-injectionproperty, a layer that contains a bipolar substance (a substance havinga high electron- and hole-transport property), and the like. Forexample, the EL layer 103 can be fanned as appropriate by combining ahole-injection layer, a hole-transport layer, a light-emitting layer, anelectron-transport layer, an electron-injection layer, and the like. Inthis embodiment, described is a structure in which the EL layer 103includes a hole-injection layer 111, a hole-transport layer 112, alight-emitting layer 113, and an electron-transport layer 114 stacked inthat order over the first electrode 102. Specific materials to form eachof the layers are given below.

The hole-injection layer 111 contains a substance having a highhole-injection property. Molybdenum oxide, vanadium oxide, rutheniumoxide, tungsten oxide, manganese oxide, or the like can be used.Alternatively, the hole-injection layer 111 can be formed using aphthalocyanine-based compound such as phthalocyanine (abbreviation:H₂Pc) or copper phthalocyanine (abbreviation: CuPc), an aromatic aminecompound such as4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB) orN,N′-bis[4-[bis(3-methylphenyl)amino]phenyl]-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: DNTPD), a high molecular compound such aspoly(ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS), orthe like.

Alternatively, the hole-injection layer 111 can be formed using acomposite material in which a substance having an acceptor property ismixed into a substance having a high hole-transport property. Note that,by using such a substance having an acceptor property into which asubstance having a high hole-transport property is mixed, a materialused to form an electrode may be selected regardless of its workfunction. In other words, besides a material having a high workfunction, a material having a low work function can also be used for thefirst electrode 102. As the acceptor substance,7,7,8,8-tetracyano-2,3,5,6-tetrafluoro quino dimethane (abbreviation:F₄-TCNQ), chloranil, and the like can be given. In addition, atransition metal oxide can be given. In addition, an oxide of metalsthat belong to Group 4 to Group 8 of the periodic table can be given.Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromiumoxide, molybdenum oxide, tungsten oxide, manganese oxide, and rheniumoxide are preferable because their electron-accepting property is high.Among these, molybdenum oxide is especially preferable because it isstable in the air and its hygroscopic property is low and is easilytreated.

As the substance having a high hole-transport property used for thecomposite material, any of various compounds such as an aromatic aminecompound, a carbazole derivative, an aromatic hydrocarbon, and a highmolecular compound (e.g., an oligomer, a dendrimer, or a polymer) can beused. The organic compound used for the composite material is preferablyan organic compound having a high hole-transport property. Specifically,a substance having a hole mobility of 10⁻⁶ cm²/Vs or higher ispreferably used. Note that other than these substances, any substancethat has a property of transporting more holes than electrons may beused. An organic compound which can be used as a substance having a highhole-transport property in the composite material is specifically givenbelow.

Examples of the aromatic amine compound includeN,N′-di(p-tolyl)-N,N′-diphenyl-p-phenylenediamine (abbreviation:DTDPPA), 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl(abbreviation: DPAB),N,N′-bis[4-[bis(3-methylphenyl)amino]phenyl]-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: DNTPD),1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B), and the like.

Examples of the carbazole derivative which can be used for the compositematerial specifically include3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2),3[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1), and the like.

Examples of the carbazole derivative which can be used for the compositematerial also include 4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB),9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA),1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene, and thelike.

Examples of the aromatic hydrocarbon which can be used for the compositematerial include 2-tert-butyl-9,10-di(2-naphthyl)anthracene(abbreviation: t-BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA),2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA),9,10-di(2-naphthyl)anthracene (abbreviation: DNA),9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene(abbreviation: t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene(abbreviation: DMNA),2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene,9,10-bis[2-(1-naphthyl)phenyl]anthracene,2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene,2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl,10,10′-diphenyl-9,9′-bianthryl,10,10′-bis(2-phenylphenyl)-9,9′-bianthryl,10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene,tetracene, rubrene, perylene, and 2,5,8,11-tetra(tert-butyl)perylene.Besides, pentacene, coronene, or the like can also be used. Thus, anaromatic hydrocarbon having a hole mobility of 1×10⁻⁶ cm²/Vs or higherand having 14 to 42 carbon atoms is more preferably used.

The aromatic hydrocarbon which can be used for the composite materialmay have a vinyl skeleton. Examples of the aromatic hydrocarbon having avinyl group include 4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation:DPVBi), 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation:DPVPA), and the like.

Moreover, a high molecular compound such as poly(N-vinylcarbazole)(abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), orpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation:poly-TPD) can also be used.

Note that any of the carbazole derivatives represented by the generalformula (G1) can also be used as the organic compound in the compositematerial. The carbazole derivative represented by the general formula(G1) is preferably contained in the hole-transport layer of thelight-emitting element of this embodiment because in this case injectionof holes from the hole-injection layer to the hole-transport layer canbe smoothly performed, and thus, the driving voltage can be reduced. Forthe same reason, in the case where any of the carbazole derivativesrepresented by the general formula (G1) is used as an organic compoundin the composite material, it is more preferable that the carbazolederivative and the substance used for the hole-transport layer be thesame substance.

The hole-transport layer 112 contains a substance having a highhole-transport property. In this embodiment, any of the carbazolederivatives represented by the general formula (G1) is used for thehole-transport layer.

The light-emitting layer 113 contains a light-emitting substance. Thelight-emitting layer 113 may be formed using a film containing only alight-emitting substance or a film in which an emission center substanceis dispersed in a host material.

There is no particular limitation on a material that can be used as thelight-emitting substance or the emission center substance in thelight-emitting layer 113, and light emitted from the material may beeither fluorescence or phosphorescence. Examples of the light-emittingsubstance or the emission center substance include the following.Examples of a fluorescent substance includeN,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine(abbreviation: 2YGAPPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA), perylene, 2,5,8,11-tetra-tert-butylperylene(abbreviation: TBP),4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA),N,N″-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N′,N′-triphenyl-1,4-phenylenediamine](abbreviation: DPABPA),N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: 2PCAPPA),N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPPA),N,N,N′,N′N″,N″,N′″,N′″-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetraamine(abbreviation: DBC1), coumarin 30,N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPABPhA),9,10-bis(1,1′-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine(abbreviation: 2YGABPhA), N,N,9-triphenylanthracen-9-amine(abbreviation: DPhAPhA), coumarin 545T, N,N′-diphenylquinacridone(abbreviation: DPQd), rubrene,5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT),2-(2-{2-[4-(dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyran-4-ylidene)propanedinitrile(abbreviation: DCM1),2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCM2),N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation:p-mPhTD),7,14-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine(abbreviation: p-mPhAFD),2-{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTI),2-{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTB),2-(2,6-bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile(abbreviation: BisDCM), and2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: BisDCJTM). Examples of a phosphorescent substance includebis[2-(3′,5′-bistrifluoromethylphenyl)pyridinato-N,C^(2′)]iridium(III)picolinate (abbreviation: Ir(CF₃ ppy)₂(pic)),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate (abbreviation: FIracac),tris(2-phenylpyridinato)iridium(III) (abbreviation: Ir(ppy)₃),bis(2-phenylpyridinato)iridium(III) acetylacetonate (abbreviation:Ir(ppy)₂(acac)), tris(acetylacetonato)(monophenanthroline)terbium(III)(abbreviation: Tb(acac)₃(Phen)) bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation: Ir(bzq)₂(acac)),bis(2,4-diphenyl-1,3-oxazolato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(dpo)₂(acac)),bis[2-(4′-perfluorophenylphenyl)pyridinato]iridium(III) acetylacetonate(abbreviation: Ir(p-PF-ph)₂(acac)),bis(2-phenylbenzothiazolato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(bt)₂(acac)),bis[2-(2′-benzo[4,5-α]thienyppyridinato-N,C^(3′)]iridium(acetylacetonate)(abbreviation: Ir(btp)₂(acac)),bis(1-phenylisoquinolinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(piq)₂(acac)),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: Ir(Fdpq)₂(acac)),(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(acac)),2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum(II)(abbreviation: PtOEP),tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III)(abbreviation: Eu(DBM)₃(Phen)), andtris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III)(abbreviation: Eu(TTA)₃(Phen)).

There is no particular limitation on a material that can be used as theabove host material, and for example, a metal complex, a heterocycliccompound, or an aromatic amine compound can be used. Examples of themetal complex include tris(8-quinolinolato)aluminum(III) (abbreviation:Alq), tris(4-methyl-8-quinolinolato)aluminum(III) (abbreviation: Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III)(abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq),bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO),bis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ), andthe like. Examples of the heterocyclic compounds include2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI), bathophenanthroline (abbreviation: BPhen),bathocuproine (abbreviation: BCP),9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation:CO11), and the like. Examples of the aromatic amine compound include4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPD),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD),4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), and the like. In addition, a condensed polycyclicaromatic compound such as an anthracene derivative, a phenanthrenederivative, a pyrene derivative, a chrysene derivative, and adibenzo[g,p]chrysene derivative can be used. Specific examples of thecondensed polycyclic aromatic compound include 9,10-diphenylanthracene(abbreviation: DPAnth),N,N-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: CzA1PA), 4-(10-phenyl-9-anthryl)triphenylamine(abbreviation: DPhPA),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA),N,9-diphenyl-N-{4-[4-(10-phenyl-9-anthryl)phenyl]phenyl}-9H-carbazol-3-amine(abbreviation: PCAPBA),N,9-diphenyl-N-(9,10-diphenyl-2-anthryl)-9H-carbazol-3-amine(abbreviation: 2PCAPA), 6,12-dimethoxy-5,11-diphenylchrysene,N,N,N′,N′,N″,N″,N′″,N′″-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetramine(abbreviation: DBC1), 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: CzPA),3,6-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: DPCzPA), 9,10-bis(3,5-diphenylphenyl)anthracene(abbreviation: DPPA), 9,10-di(2-naphthyl)anthracene (abbreviation: DNA),2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA),9,9′-bianthryl (abbreviation: BANT),9,9′-(stilbene-3,3′-diyl)diphenanthrene (abbreviation: DPNS),9,9′-(stilbene-4,4′-diyl)diphenanthrene (abbreviation: DPNS2),3,3′,3″-(benzene-1,3,5-triyl)tripyrene (abbreviation: TPB3), and thelike. One or more substances having a wider energy gap than theabove-described emission center substance may be selected from thesesubstances and known substances. Moreover, in the case where theemission center substance emits phosphorescence, a substance havinghigher triplet excitation energy (energy difference between a groundstate and a triplet excitation state) than the emission center substancemay be selected as the host material.

The light-emitting layer 113 may be a stack of two or more layers. Forexample, in the case where the light-emitting layer 113 is formed bystacking a first light-emitting layer and a second light-emitting layerin that order over the hole-transport layer, for example, the firstlight-emitting layer is formed using a substance having a hole-transportproperty as the host material and the second light-emitting layer isformed using a substance having an electron-transport property as thehost material.

In the case where the light-emitting layer having the above-describedstructure is formed using a plurality of materials, the light-emittinglayer can be formed using co-evaporation by a vacuum evaporation method;or an inkjet method, a spin coating method, a dip coating method, or thelike as a method of mixing a solution.

The electron-transport layer 114 contains a substance having a highelectron-transport property. For example, a layer containing a metalcomplex having a quinoline skeleton or a benzoquinoline skeleton, suchas tris(8-quinolinolato)aluminum (abbreviation: Alq),tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃),bis(10-hydroxybenzo[h]-quinolinato)beryllium (abbreviation: BeBq₂), orbis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq), or the like can be used. Alternatively, a metal complex having anoxazole-based or thiazole-based ligand, such asbis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: Zn(BOX)₂) orbis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation: Zn(BTZ)₂), orthe like can be used. Besides the metal complexes,2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ), bathophenanthroline (abbreviation: BPhen),bathocuproine (abbreviation: BCP), or the like can also be used. Thesubstances mentioned here mainly have an electron mobility of 10⁻⁶cm²/Vs or higher. Note that other than these substances, any substancethat has a property of transporting more electrons than holes may beused.

Furthermore, the electron-transport layer is not limited to a singlelayer, and two or more layers containing the above-described substancesmay be stacked.

Further, a layer that controls transport of electron carriers may beprovided between the electron-transport layer and the light-emittinglayer. Specifically, the layer that controls transport of electroncarriers is a layer formed by adding a small amount of substance havinga high electron-trapping property to the material having a highelectron-transport property as described above, so that carrier balancecan be adjusted. Such a structure is very effective in suppressing aproblem (such as shortening of element lifetime) caused when electronspass through the light-emitting layer.

In addition, an electron-injection layer may be provided between theelectron-transport layer and the second electrode 104, in contact withthe second electrode 104. As the electron-injection layer, an alkalimetal, an alkaline earth metal, or a compound thereof such as lithiumfluoride (LiF), cesium fluoride (CsF), or calcium fluoride (CaF₂) can beused. For example, a layer that is formed using a substance having anelectron-transport property and contains an alkali metal, an alkalineearth metal, or a compound thereof, such as an Alq layer containingmagnesium (Mg), may be used. A layer that is formed using a substancehaving an electron-transport property and contains an alkali metal or analkaline earth metal is more preferably used as the electron-injectionlayer because electrons from the second electrode 104 is efficientlyinjected.

The second electrode 104 can be formed using a metal, an alloy, anelectrically conductive compound, a mixture of them, or the like havinga low work function (specifically, a work function of 3.8 eV or lower).Specific examples of such a cathode material include an elementbelonging to Group 1 or 2 in the periodic table, i.e., an alkali metalsuch as lithium (Li) or cesium (Cs), or an alkaline earth metal such asmagnesium (Mg), calcium (Ca), or strontium (Sr); an alloy containing anyof them (e.g., MgAg or AlLi); a rare earth metal such as europium (Eu)or ytterbium (Yb); an alloy containing such a rare earth metal; and thelike. However, when the electron-injection layer is provided between thesecond electrode 104 and the electron-transport layer, the secondelectrode 104 can be formed using any of a variety of conductivematerials such as Al, Ag, ITO, or indium oxide-tin oxide containingsilicon or silicon oxide regardless of its work function. Films of theseconductive materials can be foamed by a sputtering method, an inkjetmethod, a spin coating method, or the like.

Further, any of a variety of methods can be employed for forming the ELlayer 103 regardless of a dry process or a wet process. For example, avacuum evaporation method, an inkjet method, a spin coating method orthe like may be used. A different formation method may be employed foreach electrode or each layer.

In addition, the electrode may be foamed by a wet method using a sol-gelmethod, or by a wet method using paste of a metal material.Alternatively, the electrode may be formed by a dry method such as asputtering method or a vacuum evaporation method.

In the light-emitting element having the above-described structure, acurrent flows due to a potential difference made between the firstelectrode 102 and the second electrode 104, a hole and an electron arerecombined in the light-emitting layer 113, which contains a substancehaving a high light-emitting property, and light is emitted. That is, alight-emitting region is formed in the light-emitting layer 113.

The emitted light is extracted out through one or both of the firstelectrode 102 and the second electrode 104. Therefore, one or both ofthe first electrode 102 and the second electrode 104 arelight-transmitting electrodes. In the case where only the firstelectrode 102 is a light-transmitting electrode, the emitted light isextracted from the substrate side through the first electrode 102. Inthe case where only the second electrode 104 is a light-transmittingelectrode, the emitted light is extracted from the side opposite to thesubstrate side through the second electrode 104. In a case where each ofthe first electrode 102 and the second electrode 104 is alight-transmitting electrode, the emitted light is extracted from boththe substrate side and the side opposite to the substrate through thefirst electrode 102 and the second electrode 104.

The structure of the layers provided between the first electrode 102 andthe second electrode 104 is not limited to the above-describedstructure. However, a structure in which a light-emitting region forrecombination of holes and electrons is positioned away from the firstelectrode 102 and the second electrode 104 so as to prevent quenchingdue to the proximity of the light-emitting region and a metal used forelectrodes and carrier-injection layers is preferable. The order ofstacking the layers is not limited thereto, and the following order,which is opposite to that in FIG. 1A, may be employed: the secondelectrode, the electron-injection layer, the electron-transport layer,the light-emitting layer, the hole-transport layer, the hole-injectionlayer, and the first electrode over the substrate.

In addition, as for the hole-transport layer or the electron-transportlayer in direct contact with the light-emitting layer, particularly acarrier-transport layer in contact with a side closer to alight-emitting region in the light-emitting layer 113, in order tosuppress energy transfer from an exciton which is generated in thelight-emitting layer, it is preferable that the energy gap thereof bewider than the energy gap of the light-emitting substance contained inthe light-emitting layer or the energy gap of the emission centersubstance contained in the light-emitting layer.

Since the light-emitting element of this embodiment uses any of thecarbazole derivatives represented by the general formula (G1), which hasa wide energy gap, for the hole-transport layer, the light-emittingelement can emit light efficiently even when the light-emittingsubstance or the emission center substance is a substance that has awide energy gap and emits blue fluorescence or a substance that has hightriplet excitation energy (energy difference between a ground state anda triplet excited state) and emits green phosphorescence; thus, alight-emitting element with high emission efficiency can be provided.Accordingly, a light-emitting element having lower power consumption canbe provided. In addition, a light-emitting element that emits light withhigh color purity can be provided. Further, any of the carbazolederivatives represented by the general formula (G1) is excellent in acarrier-transport property; therefore, a light-emitting element drivenwith a low driving voltage can be provided.

In this embodiment, the light-emitting element is formed over asubstrate formed of glass, plastic, or the like. By fabricating aplurality of such light-emitting elements over one substrate, a passivematrix light-emitting device can be fabricated. In addition, forexample, a thin film transistor (TFT) may be formed over a substrateformed of glass, plastic, or the like, and a light-emitting element maybe fabricated over an electrode electrically connected to the TFT. Inthis way, an active matrix light-emitting device in which the TFTcontrols the drive of the light-emitting element can be fabricated. Notethat there is no particular limitation on the structure of the TFT.Either a staggered TFT or an inverted staggered TFT may be employed. Inaddition, crystallinity of a semiconductor used for the TFT is notparticularly limited either; an amorphous semiconductor or a crystallinesemiconductor may be used. In addition, a driver circuit formed over aTFT substrate may be constructed from both n-channel and p-channel TFTsor from one of n-channel and p-channel TFTs.

Embodiment 2

In this embodiment, a light-emitting element having a differentstructure from that described in Embodiment 1 is described.

Described is a structure in which light is emitted from an emissioncenter substance having a light-emitting property by forming alight-emitting layer 113 described in Embodiment 1 in such a way thatthe emission center substance having a light-emitting property isdispersed into any of the carbazole derivatives represented by thegeneral formula (G1), i.e., a structure in which the carbazolederivative represented by the general formula (G1) is used as a hostmaterial of the light-emitting layer 113.

Each carbazole derivative represented by the general formula (G1) has awide energy gap or high triplet excitation energy (energy differencebetween a ground state and a triplet excited state), and thus can makeanother light-emitting substance excited and emit light effectively;therefore, any of the carbazole derivatives represented by the generalformula (G1) can be suitably used as the host material and lightemission that originates from the light-emitting substance can beobtained. Thus, a light-emitting element having high emission efficiencywith small energy loss can be provided. In addition, a light-emittingelement that can easily provide light emission of a desired color thatoriginates from the emission center substance can be provided.Accordingly, a light-emitting element capable of easily emitting lightwith high color purity can be provided. Further, any of the carbazolederivatives represented by the general formula (G1) is excellent in acarrier-transport property; therefore, a light-emitting element drivenwith a low driving voltage can also be provided.

Here, there is no particular limitation on the emission center substancedispersed into any of the carbazole derivatives represented by thegeneral formula (G1), and any of various materials can be used.Specifically, it is possible to use4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran(abbreviation: DCM1),4-(dicyanomethylene)-2-methyl-6-(julolidin-4-yl-vinyl)-4H-pyran(abbreviation: DCM2), N,N-dimethylquinacridone (abbreviation: DMQd),9,10-diphenylanthracene (abbreviation: DPA), 5,12-diphenyltetracene(abbreviation: DPT), coumarin 6, perylene, rubrene,N,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenylpyrene-1,6-diamine(abbreviation: 1,6FLPAPm), or another known fluorescent substance thatemits fluorescence. Alternatively, it is possible to usebis(2-phenylbenzothiazolato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(bt)₂(acac)),tris(2-phenylquinolinato-N,C^(2′))iridium(III) (abbreviation: Ir(pq)₃),bis(2-phenylquinolinato-N,C^(2′))iridium(III)(acetylacetonate)(abbreviation: Ir(pq)₂(acac)),bis[2-(2′-benzo[4,5-α]thienyl)pyridinato-N,C^(3′)]iridium(III)acetylacetonate (abbreviation: Ir(btp)₂(acac)),bis(1-phenylisoquinolinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(piq)₂(acac)),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: Ir(Fdpq)₂(acac)),tris(2-phenylpyridinato-N,C^(2′))iridium(III) (abbreviation: Ir(ppy)₃),or 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum(II)(abbreviation: PtOEP), or another known phosphorescent substance thatemits phosphorescence. In the case where any of the carbazolederivatives represented by the general formula (G1) has a light-emittingproperty, the carbazole derivative can be used as the emission centersubstance. In that case, the carbazole derivative used as the hostmaterial and the carbazole derivative used as the emission centersubstance are preferably different from each other. Among theabove-described substances or known substances, a substance that has anarrower band gap or lower triplet excitation energy than any of thecarbazole derivatives represented by the general formula (G1), which isused as the host material, is selected as the emission center substance.

Further, another organic compound may be dispersed at the same time inthe light-emitting layer, in addition to any of the carbazolederivatives represented by the general formula (G1) and the emissioncenter substance dispersed into the carbazole derivative. In this case,a substance that improves carrier balance of the light-emitting layer ispreferably used, such as the above-described substances having a highelectron-transport property.

The carbazole derivative represented by the following general formula(G1) described in Embodiment 1 becomes a bipolar substance depending onthe structure of Ar in the formula. By use of the bipolar carbazolederivative represented by the general formula (G1) as a host materialfor a light-emitting element, a light-emitting region can be dispersed,and a reduction in emission efficiency due to concentration quenching orT-T annihilation can be suppressed; thus, a light-emitting elementhaving higher emission efficiency can be provided. Further, thelight-emitting layer becomes a bipolar layer, so that the drivingvoltage can be more easily reduced in the light-emitting element thanin, a light-emitting element including a monopolar light-emitting layer.

In the formula, Ar represents an aryl group having 6 to 70 carbon atomsor a heteroaromatic group having 1 to 70 carbon atoms. In addition, R⁰represents a group represented by the following general formula (g1),and R⁸ represents any one of hydrogen, an alkyl group having 1 to 6carbon atoms, an aryl group having 6 to 15 carbon atoms, and a grouprepresented by the following general formula (g2). Note that thesubstitution site of R⁰ is a carbon atom represented by either α or β,and the substitution site of R⁸ is a carbon atom represented by either γor δ.

(In the formula, X¹ represents oxygen or sulfur, and R¹ to R⁷individually represent any one of hydrogen, an alkyl group having 1 to 6carbon atoms, and an aryl group having 6 to 15 carbon atoms.)

(In the formula, X² represents oxygen or sulfur, and R⁹ to R¹⁵individually represent any one of hydrogen, an aryl group having 6 to 15carbon atoms, and an alkyl group having 1 to 6 carbon atoms.)

In order that any of the carbazole derivatives represented by the abovegeneral formula (G1) be bipolar, an aryl group having a π-electrondeficient heteroaromatic ring group or a heteroaromatic ring group, forexample, should be applied to a substituent represented by Ar above;that is, Ar should contain a skeleton having an electron-transportproperty. Specific examples thereof are an aryl group having abenzimidazolyl group, a heteroaromatic ring group having abenzimidazolyl group, an aryl group having a benzoxazolyl group, aheteroaromatic ring group having a benzoxazolyl group, an aryl grouphaving an oxadiazolyl group, a heteroaromatic ring group having anoxadiazolyl group, and the like.

Note that, regarding the layers other than the light-emitting layer 113,the structure described in Embodiment 1 can be applied as appropriate.Further, the hole-transport layer 112 can be formed using any of thematerials given as the substances having a high hole-transport propertywhich can be used in a composite material in Embodiment 1. Besides, thehole-transport layer 112 can be formed using a substance having a highhole-transport property such as the following aromatic amine compounds:4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine(abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA), or4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB); or the like. Needless to say, any of the carbazolederivatives represented by the general formula (G1) can also be used.The substances mentioned here mainly have a hole mobility of 10⁻⁶ cm²/Vsor higher. Note that other than these substances, any substance that hasa property of transporting more holes than electrons may be used. Notethat the layer containing a substance having a high hole-transportproperty is not limited to a single layer, and two or more layerscontaining the above-described substances may be stacked.

Alternatively, a high molecular compound such as poly(N-vinylcarbazole)(abbreviation: PVK) or poly(4-vinyltriphenylamine) (abbreviation: PVTPA)can be used for the hole-transport layer 112.

Embodiment 3

In this embodiment, an embodiment of a light-emitting element with astructure in which a plurality of light-emitting units are stacked(hereinafter this type of light-emitting element is also referred to asa stacked element) is described with reference to FIG. 1B. Thislight-emitting element includes a plurality of light-emitting unitsbetween a first electrode and a second electrode. Each light-emittingunit can have a structure similar to that of an EL layer 103 describedin Embodiment 1 or 2. That is, a light-emitting element described inEmbodiment 1 or 2 includes a single light-emitting unit; thelight-emitting element in this embodiment includes a plurality oflight-emitting units.

In FIG. 1B, a first light-emitting unit 511 and a second light-emittingunit 512 are stacked between a first electrode 501 and a secondelectrode 502, and a charge generation layer 513 is provided between thefirst light-emitting unit 511 and the second light-emitting unit 512.The first electrode 501 and the second electrode 502 correspond to afirst electrode 102 and a second electrode 104 in Embodiment 1,respectively, and electrodes similar to those described in Embodiment 1can be applied to the first electrode 501 and the second electrode 502.Further, the first light-emitting unit 511 and the second light-emittingunit 512 may have the same structure or different structures.

The charge generation layer 513 contains a composite material of anorganic compound and a metal oxide. This composite material of anorganic compound and a metal oxide is described in Embodiment 1 andcontains an organic compound and a metal oxide such as vanadium oxide,molybdenum oxide, or tungsten oxide. As the organic compound, any ofvarious compounds such as an aromatic amine compound, a carbazolederivative, an aromatic hydrocarbon, and a high molecular compound(e.g., oligomer, dendrimer, or polymer) can be used. As the organiccompound, an organic compound having a hole-transport property and ahole mobility of 10⁻⁶ cm²/Vs or higher is preferably used. Note thatother than these substances, any substance that has a property oftransporting more holes than electrons may be used. The composite of anorganic compound and a metal oxide is excellent in carrier-injectionproperty and carrier-transport property, and hence, low-voltage drivingand low-current driving can be achieved.

The charge generation layer 513 may be formed by combining a layercontaining the composite material of an organic compound and metal oxidewith a layer containing another material. For example, the layercontaining the composite material of an organic compound and a metaloxide may be combined with a layer containing a compound of a substanceselected from substances having an electron-donating property and acompound having a high electron-transport property. Moreover, the layercontaining the composite material of an organic compound and a metaloxide may be combined with a transparent conductive film.

The charge generation layer 513 interposed between the firstlight-emitting unit 511 and the second light-emitting unit 512 may haveany structure as far as electrons can be injected to a light-emittingunit on one side and holes can be injected to a light-emitting unit onthe other side when a voltage is applied between the first electrode 501and the second electrode 502. For example, in FIG. 1B, any layer can beemployed as the charge generation layer 513 as far as the layer injectselectrons into the first light-emitting unit 511 and holes into thesecond light-emitting unit 512 when a voltage is applied such that thepotential of the first electrode is higher than that of the secondelectrode.

Although the light-emitting element having two light-emitting units isdescribed in this embodiment, the present invention can be similarlyapplied to a light-emitting element in which three or morelight-emitting units are stacked. When the charge generation layer isprovided between the pair of electrodes so as to partition the plurallight-emitting units like the light-emitting element of this embodiment,the element can have a long lifetime with high luminance while keepinglow current density. When the light-emitting element is applied forillumination, voltage drop due to resistance of an electrode materialcan be reduced, thereby achieving homogeneous light emission in a largearea. Moreover, the light-emitting device can be driven with a lowdriving voltage and consume less power.

By making emission colors of the light-emitting units different fromeach other, light of a desired color can be obtained from thelight-emitting element as a whole. For example, in a light-emittingelement including two light-emitting units, the emission colors of thefirst light-emitting unit and the second light-emitting unit are madecomplementary, so that the light-emitting element which emits whitelight as the whole element can be obtained. Note that the word“complementary” means color relationship in which an achromatic color isobtained when colors are mixed. In other words, when light ofcomplementary colors is mixed, white light emission can be obtained. Thesame can be applied to a light-emitting element including threelight-emitting units. For example, when the first light-emitting unitemits red light, the second light-emitting unit emits green light, andthe third light-emitting unit emits blue light, white light can beemitted from the light-emitting element as a whole.

Since the light-emitting element of this embodiment contains any of thecarbazole derivatives represented by the general formula (G1), alight-emitting element having high emission efficiency can be provided.In addition, a light-emitting element driven with a low driving voltagecan be provided. Further, a light-emitting element having a longlifetime can be provided. In addition, the light-emitting unitcontaining the carbazole derivative can provide light that originatesfrom the emission center substance with high color purity; therefore, itis easy to adjust the color of light emitted from the light-emittingelement as a whole.

Note that this embodiment can be combined with any of the otherembodiments as appropriate.

Embodiment 4

Next, in this embodiment, a method of synthesizing the carbazolederivative represented by the following general formula (G1) isdescribed.

In the formula, Ar represents an aryl group having 6 to 70 carbon atomsor a heteroaromatic group having 1 to 70 carbon atoms. In addition, R⁰is a substituent represented by the following general formula (g1) whichis bonded to a carbon atom represented by either α, or β. R⁸ representsany one of hydrogen, an alkyl group having 1 to 6 carbon atoms, an arylgroup having 6 to 15 carbon atoms, and a group represented by thefollowing general formula (g2), which is bonded to a carbon atomrepresented by either γ or δ.

In the formula, X¹ represents oxygen or sulfur, and R¹ to R⁷individually represent any one of hydrogen, an alkyl group having 1 to 6carbon atoms, and an aryl group having 6 to 15 carbon atoms.

In the formula (g2), X² represents oxygen or sulfur, and R⁹ to R¹⁵individually represent any one of hydrogen, an aryl group having 6 to 15carbon atoms, and an alkyl group having 1 to 6 carbon atoms.

Here, and R⁰ in the formula is a substituent represented by the abovegeneral formula (g1); therefore, the above general formula (G1) can alsobe represented by the following general formula (G1′). In the generalformula (G1′), the substitution site of the substituent corresponding tothe above general formula (g1) is a carbon atom represented by either αor β in the general formula (G1). Hereinafter, the substitution sites ofsubstituents or elements represented by Ar, R¹ to R¹⁶, X¹, and X², andsubstituents corresponding to R⁸ and the above general formula (g1) arethe same as those in the above explanation unless otherwise explained.

Instead of the above general formula (G1), the above general formula(G1′) is used to explain a synthesis method of thereof in thisembodiment.

<Synthesis Method 122

In Synthesis Method 1, a method of synthesizing a substance representedby the general formula (G1′) in which R⁸ is hydrogen (the followinggeneral formula (G1′-1)) is described.

First, a compound having a halogen group or a triflate group at the 2-or 3-position of 9H-carbazole (a compound 1) is coupled with a boronicacid compound of dibenzothiophene or a boronic acid compound ofdibenzofuran (a compound 2), so that a 9H-carbazole derivative having astructure in which the 2- or 3-position of 9H-carbazole is bonded to the4-position of dibenzothiophene or the 4-position of dibenzofuran (acompound 3) can be obtained (a reaction formula (A-1)).

In the reaction formula (A-1), X¹ represents oxygen or sulfur, X³represents a halogen group, a triflate group, or the like, X⁴ representsa boronic acid (the boronic acid may be protected by ethylene glycol orthe like), R¹ to R⁷ individually represent any one of hydrogen, an allylgroup having 1 to 6 carbon atoms, and an aryl group having 6 to 15carbon atoms. As the coupling reaction in the reaction formula (A-1), aSuzuki-Miyaura coupling reaction using a palladium catalyst or the likecan be given.

Next, the obtained 9H-carbazole derivative (the compound 3) is coupledwith a halogenated aryl (a compound 4), so that a compound (G1-1), whichis the object of the synthesis, can be obtained (a reaction formula(A-2)).

In the reaction formula (A-2), X¹ represents oxygen or sulfur, X⁵represents a halogen group or the like, R¹ to R⁷ individually representany one of hydrogen, an alkyl group having 1 to 6 carbon atoms, and anaryl group having 6 to 15 carbon atoms, and Ar represents an aryl grouphaving 6 to 70 carbon atoms or a heteroaromatic group having 1 to 70carbon atoms. As the coupling reaction in the reaction formula (A-2), aBuchwald-Hartwig reaction using a palladium catalyst, an Ullmannreaction using copper or a copper compound, or the like can be given.

<Synthesis Method 2>

In Synthesis Method 2, a method of synthesizing a substance in which R⁸in the above general formula (G1′) is a substituent represented by theabove general formula (g2) (the following general formula (G1′-2)) isdescribed.

First, a carbazole derivative having halogen groups at the 2- and7-positions of, the 3- and 6-positions of, or the 2- and 6-positions of9H-carbazole (a compound 5) is coupled with a boronic acid compound ofdibenzothiophene or a boronic acid compound of dibenzofuran (a compound2), so that a carbazole derivative (a compound 6) can be obtained (areaction formula (B-1)).

In the reaction formula (B-1), X⁶ and X⁷ individually represent ahalogen group or the like, X⁴ represents a boronic acid (the boronicacid may be protected by ethylene glycol or the like), R¹ to R⁷individually represent any of hydrogen, an alkyl group having 1 to 6carbon atoms, and an aryl group having 6 to 15 carbon atoms. X⁶ and X⁷may the same or different. As the coupling reaction in the reactionformula (B-1), a Suzuki-Miyaura coupling reaction using a palladiumcatalyst or the like can be given.

Next, the monohalide of 9H-carbazole (the compound 6) is coupled with aboronic acid compound of dibenzothiophene or a boronic acid compound ofdibenzofuran (a compound 7), so that a carbazole derivative (a compound8) can be obtained (a reaction formula (B-2)).

In the reaction formula (B-2), X⁶ represents a halogen group or thelike, X⁴ represents a boronic acid (the boronic acid may be protected byethylene glycol or the like), R¹ to R⁷ individually represent any ofhydrogen, an alkyl group having 1 to 6 carbon atoms, and an aryl grouphaving 6 to 15 carbon atoms. As the coupling reaction in the reactionformula (B-1), a Suzuki-Miyaura coupling reaction using a palladiumcatalyst or the like can be given.

Lastly, the 9H-carbazole derivative (the compound 8) is coupled with ahalogenated aryl (a compound 4), so that a compound (G1-2), which is theobject of the synthesis, can be obtained (a reaction formula (B-3)).

In the reaction formula (B-3), X¹ represents oxygen or sulfur, X⁵represents a halogen group, R¹ to R⁷ individually represent any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, and an aryl grouphaving 6 to 15 carbon atoms, and Ar represents an aryl group having 6 to70 carbon atoms or a heteroaromatic group having 1 to 70 carbon atoms.As the coupling reaction in the reaction formula (B-3), aBuchwald-Hartwig reaction using a palladium catalyst, an Ullmannreaction using copper or a copper compound, or the like can be given.With the above reaction formulae (B-1) to (B-3), a method in which adibenzothiophene skeleton or a dibenzofuran skeleton is coupled by oneequivalent is described. However, when the compounds 2 and 7 have thesame structure, two equivalents of the dibenzothiophene derivative ordibenzofuran derivative may be coupled with the 9H-carbazole derivativeat the same time.

<Synthesis Method 322

In Synthesis Method 3, a method of synthesizing a substance in which R⁸in the above general formula (G1′) is an aryl group having 6 to 15carbon atoms or an alkyl group having 1 to 6 carbon atoms (the followinggeneral formula (G1′-3)) is described.

First, a 9H-carbazole derivative in which the 2- or 3-position of9H-carbazole is substituted with an alkyl group or an aryl group and the3- or 6-position of 9H-carbazole is substituted with a halogen group (acompound 9) is coupled with a boronic acid compound of dibenzothiopheneor a boronic acid compound of dibenzofuran (a compound 2), so that a9H-carbazole derivative (a compound 10) can be obtained (a reactionformula (C-1)).

In the reaction formula (C-1), X¹ represents oxygen or sulfur, X⁹represents a halogen group, a triflate group, or the like, R¹ to R⁷individually represent any one of hydrogen, an alkyl group having 1 to 6carbon atoms, and an aryl group having 6 to 15 carbon atoms, and R¹⁶represents any of an alkyl group having 1 to 6 carbon atoms and an arylgroup having 6 to 15 carbon atoms. As the coupling reaction in thereaction formula (C-1), a Suzuki-Miyaura coupling reaction using apalladium catalyst or the like can be given.

Next, the 9H-carbazole derivative (the compound 10) is coupled with ahalogenated aryl (a compound 4), so that a compound (G1′-3), which isthe object of the synthesis, can be obtained (a reaction formula (C-2)).

In the reaction formula (C-2), X¹ represents oxygen or sulfur, X⁵represents a halogen group, R¹ to R⁷ individually represent any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, and an aryl grouphaving 6 to 15 carbon atoms, R¹⁶ represents any of an alkyl group having1 to 6 carbon atoms and an aryl group having 6 to 15 carbon atoms, andAr represents an aryl group having 6 to 70 carbon atoms or aheteroaromatic group having 1 to 70 carbon atoms.

Embodiment 5

In this embodiment, a light-emitting device including a light-emittingelement containing any of the carbazole derivatives represented by thegeneral formula (G1) is described.

In this embodiment, the light-emitting device including a light-emittingelement containing any of the carbazole derivatives represented by thegeneral formula (G1) is described with reference to FIGS. 2A and 2B.Note that FIG. 2A is a top view illustrating the light-emitting deviceand FIG. 2B is a cross-sectional view of FIG. 2A taken along lines A-Band C-D. The light-emitting device includes a driver circuit portion(source-side driver circuit) 601, a pixel portion 602, and a drivercircuit portion (gate-side driver circuit) 603 which are illustratedwith dotted lines. These units control light emission of thelight-emitting element. Moreover, a reference numeral 604 denotes asealing substrate; 605, a sealing material; and 607, a space surroundedby the sealing material 605.

Reference numeral 608 denotes a wiring for transmitting signals to beinputted into the source-side driver circuit 601 and the gate-sidedriver circuit 603 and receiving signals such as a video signal, a clocksignal, a start signal, and a reset signal from an FPC (flexible printedcircuit) 609 serving as an external input terminal. Although only theFPC is illustrated here, a printed wiring board (PWB) may be attached tothe FPC. The light-emitting device in the present specificationincludes, in its category, not only the light-emitting device itself butalso the light-emitting device provided with the FPC or the PWB.

Next, the cross-sectional structure is described with reference to FIG.2B. Although the driving circuit portion and the pixel portion areformed on an element substrate 610, the source-side driving circuit 601that is the driving circuit portion, and one of the pixels in the pixelportion 602 are illustrated here

In the source-side driver circuit 601, a CMOS circuit is formed in whichan n-channel TFT 623 and a p-channel TFT 624 are combined. Such a drivercircuit may be formed by using various circuits such as a CMOS circuit,a PMOS circuit, or an NMOS circuit. Although this embodiment shows adriver-integrated type where the driver circuit is formed over thesubstrate, the present invention is not limited to this, and the drivercircuit may be formed outside the substrate, not over the substrate.

The pixel portion 602 is formed with a plurality of pixels including aswitching TFT 611, a current controlling TFT 612, and a first electrode613 electrically connected to a drain of the current controlling TFT. Aninsulator 614 is formed so as to cover the end portions of the firstelectrode 613; here, the insulator 614 is formed using a positive typephotosensitive acrylic resin film.

In order to improve the coverage, the insulator 614 is formed to have acurved surface with curvature at its upper or lower end portion. Forexample, in the case of using positive photosensitive acrylic for theinsulator 614, only the upper end portion of the insulator 614preferably has a curved surface with a radius of curvature of 0.2 μm to0.3 μm. As the insulator 614, either a negative type which becomesinsoluble in etchant by irradiation with light or a positive type whichbecomes soluble in etchant by irradiation with light can be used.

A layer 616 containing an organic compound and a second electrode 617are formed over the first electrode 613. As a material used for thefirst electrode 613 functioning as an anode, a material having a highwork function is preferably used. For example, a single-layer film of anITO film, an indium tin oxide film containing silicon, an indium oxidefilm containing zinc oxide at 2 wt % to 20 wt %, a titanium nitridefilm, a chromium film, a tungsten film, a Zn film, a Pt film, or thelike can be used. Alternatively, a stack of a titanium nitride film anda film containing aluminum as its main component, a stack of threelayers of a titanium nitride film, a film containing aluminum as itsmain component, and a titanium nitride film, or the like can be used.Note that when a stacked structure is employed, the first electrode 613has low resistance as a wiring, forms a favorable ohmic contact, and canfunction as an anode.

In addition, the layer 616 containing an organic compound is formed byany of a variety of methods such as an evaporation method using anevaporation mask, an inkjet method, and a spin coating method. The layer616 containing an organic compound contains any of the carbazolederivatives described in Embodiment 1. Further, the layer 616 containingan organic compound may be foamed using another material such as a lowmolecular compound or a high molecular compound (the category of thehigh molecular compound includes an oligomer and a dendrimer).

As a material used for the second electrode 617, which is formed overthe layer 616 containing an organic compound and functions as a cathode,a material having a low work function (e.g., Al, Mg, Li, Ca, or an alloyor compound thereof, such as MgAg, MgIn, AlLi, LiF, or CaF₂) ispreferably used. In the case where light generated in the layer 616containing an organic compound passes through the second electrode 617,the second electrode 617 is preferably formed using a stack of a thinmetal film and a transparent conductive film (ITO, indium oxidecontaining zinc oxide at 2 wt % to 20 wt %, indium tin oxide containingsilicon, zinc oxide (ZnO), or the like).

Note that the light-emitting element is formed by the first electrode613, the layer 616 containing an organic compound, and the secondelectrode 617. The light-emitting element has any of the structuresdescribed in Embodiments 1 to 3. The pixel portion, which includes aplurality of light-emitting elements, in the light-emitting device ofthis embodiment may include both the light-emitting element with any ofthe structures described in Embodiments 1 to 3 and the light-emittingelement with a structure other than those.

Further, a light-emitting element 618 is provided in the space 607surrounded by the element substrate 610, the sealing substrate 604, andthe sealing material 605 by pasting the sealing substrate 604 and theelement substrate 610 using the sealing material 605. The space 607 maybe filled with filler, and may be filled with an inert gas (such asnitrogen or argon), the sealing material 605, or the like.

An epoxy based resin is preferably used for the sealing material 605. Itis desirable that such a material do not transmit moisture or oxygen asmuch as possible. As a material for the sealing substrate 604, a plasticsubstrate formed of FRP (fiberglass-reinforced plastics), PVF (polyvinylfluoride), polyester, acrylic, or the like can be used besides a glasssubstrate or a quartz substrate.

In this way, the light-emitting device manufactured using thelight-emitting element containing any of the carbazole derivativesrepresented by the general formula (G1) can be obtained.

Since the light-emitting device in this embodiment uses thelight-emitting element containing any of the carbazole derivativesrepresented by the general formula (G1), a light-emitting device havingfavorable characteristics can be provided. Specifically, since any ofthe carbazole derivatives described in Embodiment 1 has a wide energygap and high triplet excitation energy and can suppress energy transferfrom a light-emitting substance, a light-emitting element having highemission efficiency can be provided; thus, a light-emitting devicehaving less power consumption can be provided. In addition, since alight-emitting element driven with a low driving voltage can beprovided, a light-emitting device driven with a low driving voltage canbe provided. Further, since the light-emitting element using any of thecarbazole derivatives represented by the general formula (G1) has a longlifetime, a light-emitting device having high reliability can beprovided.

Although an active matrix light-emitting device is described in thisembodiment as described above, a passive matrix light-emitting devicemay be alternatively fabricated. FIGS. 3A and 3B illustrate a passivematrix light-emitting device fabricated according to the presentinvention. FIG. 3A is a perspective view of the light-emitting device,and FIG. 3B is a cross-sectional view taken along line X-Y in FIG. 3A.In FIGS. 3A and 3B, an electrode 952 and an electrode 956 are providedover a substrate 951, and a layer 955 containing an organic compound isprovided between the electrodes 952 and 956. An end portion of theelectrode 952 is covered with an insulating layer 953. A partition layer954 is provided over the insulating layer 953. The sidewalls of thepartition layer 954 are aslope such that the distance between bothsidewalls is gradually narrowed toward the surface of the substrate.That is, a cross section taken along the direction of the short side ofthe partition wall layer 954 is trapezoidal, and the lower side (a sidewhich is in the same direction as a plane direction of the insulatinglayer 953 and in contact with the insulating layer 953) is shorter thanthe upper side (a side which is in the same direction as the planedirection of the insulating layer 953 and not in contact with theinsulating layer 953). By providing the partition layer 954 in this way,defects of the light-emitting element due to static charge and the likecan be prevented. The passive matrix light-emitting device can also beoperated with low power consumption by including the light-emittingelement according to any of Embodiments 1 to 3 which is driven with alow driving voltage. In addition, the light-emitting device can bedriven with low power consumption by including the light-emittingelement according to any of Embodiments 1 to 3 which has high emissionefficiency. Further, the light-emitting device can have high reliabilityby including the light-emitting element according to any of Embodiments1 to 3.

Embodiment 6

In this embodiment, electronic devices of one embodiment of the presentinvention, each including the light-emitting device described inEmbodiment 5, are described. The electronic devices of the presentinvention each include a light-emitting element containing any of any ofthe carbazole derivatives represented by the general formula (G1) andthus electronic devices each having a display portion which consumesless power can be obtained. In addition, electronic devices driven witha low driving voltage can be provided. Further, electronic deviceshaving high reliability can be provided.

As examples of the electronic devices each including the light-emittingelement containing any of the carbazole derivatives represented by thegeneral formula (G1), the following can be given: cameras such as videocameras and digital cameras, goggle type displays, navigation systems,audio replay devices (e.g., car audio systems and audio systems),computers, game machines, portable information terminals (e.g., mobilecomputers, mobile phones, portable game machines, and electronic bookreaders), image replay devices in which a recording medium is provided(specifically, devices that are capable of replaying recording media,such as digital versatile discs (DVDs), and equipped with a displaydevice that can display an image), and the like. Specific examples ofthese electronic devices are illustrated in FIGS. 4A to 4D.

FIG. 4A illustrates a television device which includes a housing 9101, asupport 9102, a display portion 9103, speaker portions 9104, video inputterminals 9105, and the like. In the display portion 9103 of thistelevision device, light-emitting elements similar to those described inany of Embodiments 1 to 3 are arranged in matrix. The light-emittingelements can have high emission efficiency. In addition, alight-emitting element driven with a low driving voltage can beprovided. Further, a light-emitting element having high reliability canbe provided. Therefore, this television device having the displayportion 9103 which is formed using the light-emitting elements consumesless power. In addition, a television device driven with a low drivingvoltage can be provided. Further, a television device having highreliability can be provided.

FIG. 4B illustrates a computer according to one embodiment of thepresent invention. The computer includes a main body 9201, a housing9202, a display portion 9203, a keyboard 9204, an external connectionport 9205, a pointing device 9206, and the like. In the display portion9203 of this computer, light-emitting elements similar to thosedescribed in any of Embodiments 1 to 3 are arranged in matrix. Thelight-emitting elements can have high emission efficiency. In addition,a light-emitting element driven with a low driving voltage can beprovided. Further, a light-emitting element having high reliability canbe provided. Therefore, this computer having the display portion 9203which is formed using the light-emitting elements consumes less power.In addition, a computer driven with a low driving voltage can beprovided. Further, a computer having high reliability can be provided.

FIG. 4C illustrates a mobile phone according to one embodiment of thepresent invention. The mobile phone includes a main body 9401, a housing9402, a display portion 9403, an audio input portion 9404, an audiooutput portion 9405, operation keys 9406, an external connection port9407, an antenna 9408, and the like. In the display portion 9403 of thismobile phone, light-emitting elements similar to those described in anyof Embodiments 1 to 3 are arranged in matrix. The light-emittingelements can have high emission efficiency. In addition, alight-emitting element driven with a low driving voltage can beprovided. Further, a light-emitting element having high reliability canbe provided. Therefore, this mobile phone having the display portion9403 which is formed using the light-emitting elements consumes lesspower. In addition, a mobile phone driven with a low driving voltage canbe provided. Further, a mobile phone having high reliability can beprovided.

FIG. 4D illustrates a camera according to one embodiment of the presentinvention which includes a main body 9501, a display portion 9502, ahousing 9503, an external connection port 9504, a remote controlreceiving portion 9505, an image receiving portion 9506, a battery 9507,an audio input portion 9508, operation keys 9509, an eye piece portion9510, and the like. In the display portion 9502 of this camera,light-emitting elements similar to those described in any of Embodiments1 to 3 are arranged in matrix. The light-emitting elements can have highemission efficiency. In addition, a light-emitting element driven with alow driving voltage can be provided. Further, a light-emitting elementhaving high reliability can be provided. Therefore, this camera havingthe display portion 9502 which is formed using the light-emittingelements consumes less power. In addition, a camera driven with a lowdriving voltage can be provided. Further, a camera having highreliability can be provided.

As described above, the application range of the light-emitting devicedescribed in Embodiment 5 is so wide that the light-emitting device canbe applied to electronic devices of every field. An electronic devicewhich consumes less power can be obtained by using any of the carbazolederivatives represented by the general formula (G1). In addition, anelectronic device having a display portion capable of providinghigh-quality display with excellent color reproducibility can beobtained.

The light-emitting device described in Embodiment 5 can also be used asa lighting device. One embodiment in which the light-emitting devicedescribed in Embodiment 5 is used as a lighting device is described withreference to FIG. 5.

FIG. 5 illustrates an example of a liquid crystal display device usingthe light-emitting device described in Embodiment 5 as a backlight. Theliquid crystal display device illustrated in FIG. 5 includes a housing901, a liquid crystal layer 902, a backlight unit 903, and a housing904. The liquid crystal layer 902 is connected to a driver IC 905. Thelight-emitting device described in Embodiment 5 is used as the backlightunit 903, to which a current is supplied through a terminal 906.

With the use of the light-emitting device described in Embodiment 5 asthe backlight of the liquid crystal display device, a backlight havingless power consumption can be provided. Further, the light-emittingdevice described in Embodiment 5 is a lighting device with plane lightemission and can have a large area. Therefore, the backlight can have alarge area, and a liquid crystal display device having a large area canbe obtained. Furthermore, since the light-emitting device described inEmbodiment 5 is thin, it becomes possible to reduce the thickness of adisplay device.

FIG. 6 illustrates an example in which the light-emitting devicedescribed in Embodiment 5 is used as a table lamp which is a lightingdevice. The table lamp illustrated in FIG. 6 includes a housing 2001 anda light source 2002, and the light-emitting device described inEmbodiment 5 is used as the light source 2002.

FIG. 7 illustrates an example in which the light-emitting devicedescribed in Embodiment 5 is used as an indoor lighting device 3001.Since the light-emitting device described in Embodiment 5 consumes lesspower, a lighting device that consumes less power can be obtained.Further, since the light-emitting device described in Embodiment 5 canhave a large area, the light-emitting device can be used as a large-arealighting device. Further, since the light-emitting device described inEmbodiment 5 is thin, the light-emitting device can be used for alighting device having reduced thickness.

Example 1

In this example are described light-emitting elements according toEmbodiment 1, in which an emission center substance that emits greenphosphorescence is used for2-[4-{3-(dibenzothiophen-4-yl)-9H-carbazol-9-yl}phenyl]-1-phenylbenzimidazole(abbreviation: DBTCzBIm-II, a structural formula (1)) and2-[4-{3-(dibenzofuran-4-yl)-9H-carbazol-9-yl}phenyl]-1-phenylbenzimidazole(abbreviation: DBFCzBIm-II, a structural formula (3)), which arecarbazole derivatives, are used as host materials for the respectivelight-emitting layers.

The molecular structures of organic compounds used in this example arerepresented by the structural formulae (i) to (iv), (1), and (3) below.In the element structure in FIG. 1A, an electron-injection layer isprovided between an electron-transport layer 114 and a second electrode104.

[Fabrication of Light-Emitting Element 1 and Light-Emitting Element 2]

First, a glass substrate 101 over which indium tin oxide containingsilicon (ITSO) with a thickness of 110 nm was formed as a firstelectrode 102 was prepared. The periphery of a surface of the ITSO wascovered with a polyimide film so that an area of 2 mm×2 mm of thesurface was exposed. The electrode area was 2 mm×2 mm. As a pretreatmentfor forming the light-emitting element over the substrate, the surfaceof the substrate was washed with water and baked at 200° C. for onehour, and then a UV ozone treatment was performed for 370 seconds. Then,the substrate was transferred into a vacuum evaporation apparatus whosepressure was reduced to about 10⁻⁴ Pa, vacuum baking at 170° C. for 30minutes was performed in a heating chamber of the vacuum evaporationapparatus, and then the substrate was cooled down for about 30 minutes.

Then, the substrate was fixed on a holder provided in the vacuumevaporation apparatus such that the surface of the substrate 101provided with ITSO faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, a hole-injection layer 111 was formed by co-evaporation of4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP)represented by the above structural formula (i) and molybdenum(VI) oxidesuch that the ratio of BPAFLP:molybdenum(VI) oxide was 2:1 (weightratio). The thickness of was the layer was set to 50 nm. Note that theco-evaporation is an evaporation method in which a plurality ofdifferent substances is concurrently vaporized from the respectivedifferent evaporation sources.

Next, BPAFLP was evaporated to a thickness of 10 nm, so that ahole-transport layer 112 was formed.

Further, for the light-emitting element 1, the light-emitting layer 113was formed on the hole-transport layer 112 in such a way thatDBTCzBIm-II, which is the carbazole derivative represented by the abovestructural formula (1) and described in Embodiment1,4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation:PCBA1BP) represented by the above structural formula (ii), andtris(2-phenylpyridinato-N,C^(2′))iridium(III) (abbreviation: Ir(ppy)₃)represented by the above structural formula (iii) were evaporated toform a 20-nm-thick film so that the ratio of DBTCzBIm-II to PCBA1BP andIr(ppy)₃ was 1:0.25:0.06 (weight ratio), DBTCzBIm-II and Ir(ppy)₃ werethen evaporated to form a 20-nm-thick film so that the ratio ofDBTCzBIm-II to Ir(ppy)₃ was 1:0.06 (weight ratio), and lastlyDBTCzBIm-II was evaporated to form a 15-nm-thick film.

For the light-emitting element 2, the light-emitting layer 113 wasformed on the hole-transport layer 112 in such a way that DBFCzBIm-II,which is the carbazole derivative represented by the above structuralformula (2) and described in Embodiment 1, PCBA1BP, and Ir(ppy)₃ wereevaporated to form a 20-nm-thick film in which the ratio of DBFCzBIm-IIto PCBA1BP and Ir(ppy)₃ was 1:0.25:0.06 (weight ratio), DBFCzBIm-II toIr(ppy)₃ were then evaporated to form a 20-nm-thick film in which theratio of DBFCzBIm-II to Ir(ppy)₃ was 1:0.06 (weight ratio), and lastlyDBFCzBIm-II was evaporated to form a 15-nm-thick film.

Next, bathophenanthroline (abbreviation: BPhen) represented by the abovestructural formula (iv) was evaporated to a thickness of 15 nm, so thatan electron-transport layer 114 was formed. Further, lithium fluoridewas evaporated to a thickness of 1 nm on the electron-transport layer114, so that the electron-injection layer was formed. Lastly, analuminum film was formed to a thickness of 200 nm as the secondelectrode 104 functioning as a cathode, so that the light-emittingelements 1 and 2 were completed. Note that in the above evaporationprocesses, evaporation was all performed by a resistance heating method.

[Operation Characteristics of Light-Emitting Elements 1 and 2]

The light-emitting elements 1 and 2 thus obtained were sealed in a glovebox under a nitrogen atmosphere without being exposed to the air. Then,the operation characteristics of these light-emitting elements weremeasured. Note that the measurements were carried out at roomtemperature (in an atmosphere kept at 25° C.).

FIG. 8 shows luminance versus current density characteristics of thelight-emitting elements, FIG. 9 shows luminance versus voltagecharacteristics thereof; and FIG. 10 shows current efficiency versusluminance characteristics thereof. In FIG. 8, the vertical axisrepresents luminance (cd/m²), and the horizontal axis represents currentdensity (mA/cm²). In FIG. 9, the vertical axis represents luminance(cd/m²), and the horizontal axis represents voltage (V). In FIG. 10, thevertical axis represents current efficiency (cd/A), and the horizontalaxis represents luminance (cd/m²).

FIG. 10 reveals that the light-emitting elements in each of which thecarbazole derivative represented by the general formula (G1) is used asa host material of a light-emitting layer for emitting greenphosphorescence, has favorable luminance versus emission efficiencycharacteristics and high emission efficiency. This is because eachcarbazole derivative represented by the general formula (G1) has a wideenergy gap and high triplet excitation energy, and thus even alight-emitting substance that emits green phosphorescence gap can beefficiently excited. In addition, FIG. 8 reveals that the light-emittingelements in each of which the carbazole derivative represented by thegeneral formula (G1) is used as a host material of a light-emittinglayer for emitting green phosphorescence, has favorable luminance versusvoltage characteristics and can be driven with a low voltage. Thisindicates that each carbazole derivative represented by the generalformula (G1) has an excellent carrier-transport property.

FIG. 11 shows emission spectra when a current of 1 mA was made to flowin the fabricated light-emitting elements 1 and 2. In FIG. 11, thehorizontal axis represents emission wavelength (nm), and the verticalaxis represents emission intensity. The emission intensity is shown as avalue relative to the greatest emission intensity assumed to be 1. FIG.11 reveals that the light-emitting elements 1 and 2 each emit greenlight due to Ir(ppy)₃, which is the emission center substance.

Next, the initial luminance is set at 1000 cd/m², these elements weredriven under a condition where the current density was constant, andchanges in luminance with respect to the driving time were examined.FIG. 12 shows normalized luminance versus time characteristics. FromFIG. 12, it is found that each of the light-emitting elements 1 and 2shows favorable characteristics and has high reliability.

Example 2

In this example described are light-emitting elements according toEmbodiment 1, in which an emission center substance that emits greenphosphorescence is used for light-emitting layers and3-(dibenzothiophen-4-yl)-9-(triphenylen-2-yl)-9H-carbazole(abbreviation: DBTCzTp-II, a structural formula (5)) and3-(dibenzofuran-4-yl)-9-(triphenylen-2-yl)-9H-carbazole (abbreviation:DBFCzTp-II, a structural formula (6)), which are carbazole derivatives,are used as host materials for the respective light-emitting layers.

The molecular structures of organic compounds used in this example arerepresented by the structural formulae (i), (iv), (5), and (6) below. Inthe element structure in FIG. 1A, an electron-injection layer isprovided between an electron-transport layer 114 and a second electrode104.

[Fabrication of Light-Emitting Element 3 and Light-Emitting Element 4]

First, a glass substrate 101 over which indium tin oxide containingsilicon (ITSO) with a thickness of 110 nm was formed as a firstelectrode 102 was prepared. The periphery of a surface of the ITSO wascovered with a polyimide film so that an area of 2 mm×2 mm of thesurface was exposed. The electrode area was 2 mm×2 mm. As a pretreatmentfor forming the light-emitting element over the substrate, the surfaceof the substrate was washed with water and baked at 200° C. for onehour, and then a UV ozone treatment was performed for 370 seconds. Then,the substrate was transferred into a vacuum evaporation apparatus whosepressure was reduced to about 10⁻⁴ Pa, vacuum baking at 170° C. for 30minutes was performed in a heating chamber of the vacuum evaporationapparatus, and then the substrate was cooled down for about 30 minutes.

Then, the substrate was fixed on a holder provided in the vacuumevaporation apparatus such that the surface of the substrate 101provided with ITSO faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, a hole-injection layer 111 was formed by co-evaporation of4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP)represented by the above structural formula (i) and molybdenum(VI) oxidesuch that the ratio of BPAFLP:molybdenum(VI) oxide was 2:1 (weightratio). The thickness of was the layer was set to 50 nm. Note that theco-evaporation is an evaporation method in which a plurality ofdifferent substances is concurrently vaporized from the respectivedifferent evaporation sources.

Next, BPAFLP was evaporated to a thickness of 10 nm, so that ahole-transport layer 112 was formed.

Further, for the light-emitting element 3, the light-emitting layer 113was formed on the hole-transport layer 112 in such a way thatDBTCzTp-II, which is the carbazole derivative represented by the abovestructural formula (5) and described in Embodiment 1, andtris(2-phenylpyridinato-N,C^(2′))iridium(III) (abbreviation: Ir(ppy)₃)represented by the above structural formula (iii) were evaporated toform a 40-nm-thick film so that the ratio of DBTCzTp-II to Ir(ppy)₃ was1:0.06 (weight ratio) and then a 15-nm-thick DBTCzTp-II film.

For the light-emitting element 4, the light-emitting layer 113 wasformed on the hole-transport layer 112 in such a way that DBFCzTp-II,which is the carbazole derivative represented by the above structuralformula (6) and described in Embodiment 1, and Ir(ppy)₃ were evaporatedto form a 40-nm-thick film so that the ratio of DBFCzTp-II to Ir(ppy)₃was 1:0.06 (weight ratio) and then DBFCzTp-II was evaporated to form a15-nm-thick film.

Next, on the light-emitting layer 113, bathophenanthroline(abbreviation: BPhen) represented by the above structural formula (iv)was evaporated to a thickness of 15 nm, so that the electron-transportlayer 114 was formed. Further, lithium fluoride was evaporated to athickness of 1 nm on the electron-transport layer 114, so that theelectron-injection layer was formed. Lastly, an aluminum film was formedto a thickness of 200 nm as the second electrode 104 functioning as acathode, so that the light-emitting elements 3 and 4 were completed.Note that in the above evaporation processes, evaporation was allperformed by a resistance heating method.

[Operation Characteristics of Light-Emitting Elements 3 and 4]

The light-emitting elements 3 and 4 thus obtained were sealed in a glovebox under a nitrogen atmosphere without being exposed to the air. Then,the operation characteristics of these light-emitting elements weremeasured. Note that the measurements were carried out at roomtemperature (in an atmosphere kept at 25° C.).

FIG. 13 shows luminance versus current density characteristics of thelight-emitting elements, FIG. 14 shows luminance versus voltagecharacteristics thereof, and FIG. 15 shows current efficiency versusluminance characteristics thereof. In FIG. 13, the vertical axisrepresents luminance (cd/m²), and the horizontal axis represents currentdensity (mA/cm²). In FIG. 14, the vertical axis represents luminance(cd/m²), and the horizontal axis represents voltage (V). In FIG. 15, thevertical axis represents current efficiency (cd/A), and the horizontalaxis represents luminance (cd/m²).

FIG. 15 reveals that the light-emitting elements in each of which thecarbazole derivative represented by the general formula (G1) is used asa host material of a light-emitting layer for emitting greenphosphorescence, has favorable luminance versus emission efficiencycharacteristics and high emission efficiency. This is because eachcarbazole derivative represented by the general formula (G1) has a wideenergy gap and high triplet excitation energy, and thus even alight-emitting substance that emits green phosphorescence gap can beefficiently excited. In addition, FIG. 13 reveals that thelight-emitting elements in each of which the carbazole derivativerepresented by the general formula (G1) is used as a host material of alight-emitting layer for emitting green phosphorescence, has favorableluminance versus voltage characteristics and can be driven with a lowvoltage. This indicates that each carbazole derivative represented bythe general formula (G1) has an excellent carrier-transport property.

FIG. 16 shows emission spectra when a current of 1 mA was made to flowin the fabricated light-emitting elements 3 and 4. In FIG. 16, thehorizontal axis represents emission wavelength (nm), and the verticalaxis represents emission intensity. The emission intensity is shown as avalue relative to the greatest emission intensity assumed to be 1. FIG.16 reveals that the light-emitting elements 3 and 4 each emit greenlight due to Ir(ppy)₃, which is the emission center substance.

Next, the initial luminance is set at 1000 cd/m², these elements weredriven under a condition where the current density was constant, andchanges in luminance with respect to the driving time were examined.FIG. 17 shows normalized luminance versus time characteristics. FromFIG. 17, it is found that each of the light-emitting elements 3 and 4shows favorable characteristics and has high reliability.

Example 3

In this example described are light-emitting elements in which anemission center substance that emits blue fluorescence is used forlight-emitting layers and3-(dibenzothiophen-4-yl)-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: DBTCzPA-II, a structural formula (7)) and3-(dibenzofuran-4-yl)-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: DBFCzPA-II, a structural formula (8)), which arecarbazole derivatives represented by the general formula (G1), are usedas host materials for the respective light-emitting layers.

The molecular structures of organic compounds used in this example arerepresented by the structural formulae (iv) to (vi), (7), and (8) below.In the element structure in FIG. 1A, an electron-injection layer isprovided between an electron-transport layer 114 and a second electrode104.

[Fabrication of Light-Emitting Element 5 and Light-Emitting Element 6]

First, a glass substrate 101 over which indium tin oxide containingsilicon (ITSO) with a thickness of 110 nm was formed as a firstelectrode 102 was prepared. The periphery of a surface of the ITSO wascovered with a polyimide film so that an area of 2 mm×2 mm of thesurface was exposed. The electrode area was 2 mm×2 mm. As a pretreatmentfor forming the light-emitting element over the substrate, the surfaceof the substrate was washed with water and baked at 200° C. for onehour, and then a UV ozone treatment was performed for 370 seconds. Then,the substrate was transferred into a vacuum evaporation apparatus whosepressure was reduced to about 10⁻⁴ Pa, vacuum baking at 170° C. for 30minutes was performed in a heating chamber of the vacuum evaporationapparatus, and then the substrate was cooled down for about 30 minutes.

Then, the substrate was fixed on a holder provided in the vacuumevaporation apparatus such that the surface of the substrate 101provided with ITSO faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, a hole-injection layer 111 was formed by co-evaporation of9-[4-(9-phenylcarbazol-3-yl)]phenyl-10-phenylanthracene (abbreviation:PCzPA) represented by the above structural formula (v) andmolybdenum(VI) oxide such that the ratio of PCzPA:molybdenum(VI) oxidewas 2:1 (weight ratio). The thickness of was the layer was set to 50 nm.Note that the co-evaporation is an evaporation method in which aplurality of different substances is concurrently vaporized from therespective different evaporation sources.

Next, PCzPA was evaporated to a thickness of 10 nm, so that ahole-transport layer 112 was formed.

Further, for the light-emitting element 5, the light-emitting layer 113was formed on the hole-transport layer 112 in such a way thatDBTCzPA-II, which is the carbazole derivative represented by the abovestructural formula (7) and described in Embodiment 1, andN,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenyl-pyrene-1,6-diamine(abbreviation: 1,6FLPAPm) represented by the above structural formula(vi) were evaporated to form a 30-nm-thick film so that the ratio ofDBTCzPA-II to 1,6FLPAPrn was 1:0.05 (weight ratio).

For the light-emitting element 6, the light-emitting layer 113 wasformed on the hole-transport layer 112 in such a way that DBFCzPA-II,which is the carbazole derivative represented by the above structuralformula (8) and described in Embodiment 1, and 1,6FLPAPrn wereevaporated to form a 30-nm-thick film so that the ratio of DBFCzPA-II to1,6FLPAPrn was 1:0.05 (weight ratio).

Next, on the light-emitting layer 113,tris(8-quinolinolato)aluminum(III) (abbreviation: Alq) represented bythe above structural formula (vii) was evaporated to a thickness of 10nm, and then bathophenanthroline (abbreviation: BPhen) represented bythe above structural formula (iv) was evaporated to a thickness of 15nm, so that the electron-transport layer 114 was formed. Further,lithium fluoride was evaporated to a thickness of 1 nm on theelectron-transport layer 114, so that the electron-injection layer wasformed. Lastly, an aluminum film was formed to a thickness of 200 nm asthe second electrode 104 functioning as a cathode, so that thelight-emitting elements 5 and 6 were completed. Note that in the aboveevaporation processes, evaporation was all performed by a resistanceheating method.

[Operation Characteristics of Light-Emitting Elements 5 and 6]

The light-emitting elements 5 and 6 thus obtained were sealed in a glovebox under a nitrogen atmosphere without being exposed to the air. Then,the operation characteristics of these light-emitting elements weremeasured. Note that the measurements were carried out at roomtemperature (in an atmosphere kept at 25° C.).

FIG. 18 shows luminance versus current density characteristics of thelight-emitting elements, FIG. 19 shows luminance versus voltagecharacteristics thereof, and FIG. 20 shows current efficiency versusluminance characteristics thereof. In FIG. 18, the vertical axisrepresents luminance (cd/m²), and the horizontal axis represents currentdensity (mA/cm²). In FIG. 19, the vertical axis represents luminance(cd/m²), and the horizontal axis represents voltage (V). In FIG. 20, thevertical axis represents current efficiency (cd/A), and the horizontalaxis represents luminance (cd/m²).

FIG. 20 reveals that the light-emitting elements in each of which thecarbazole derivative represented by the general formula (G1) is used asa host material of a light-emitting layer for emitting bluefluorescence, has favorable luminance versus emission efficiencycharacteristics and high emission efficiency. This is because eachcarbazole derivative represented by the general formula (G1) has a wideenergy gap, and thus even a light-emitting substance that emits bluefluorescence and has a wide energy gap can be efficiently excited. Inaddition, FIG. 18 reveals that the light-emitting elements in each ofwhich the carbazole derivative represented by the general formula (G1)is used as a host material of a light-emitting layer for emitting bluefluorescence, has favorable luminance versus voltage characteristics andcan be driven with a low voltage. This indicates that each carbazolederivative represented by the general formula (G1) has an excellentcarrier-transport property.

FIG. 21 shows emission spectra when a current of 1 mA was made to flowin the fabricated light-emitting elements. In FIG. 21, the horizontalaxis represents emission wavelength (nm), and the vertical axisrepresents emission intensity. The emission intensity is shown as avalue relative to the greatest emission intensity assumed to be 1. FIG.21 reveals that the light-emitting elements 5 and 6 each emit blue lightdue to 1,6FLPAPm, which is the emission center substance.

Next, the initial luminance is set at 1000 cd/m², these elements weredriven under a condition where the current density was constant, andchanges in luminance with respect to the driving time were examined.FIG. 22 shows normalized luminance versus time characteristics of thelight-emitting elements. From FIG. 22, it is found that each of thelight-emitting elements 5 and 6 shows favorable characteristics and hashigh reliability.

Example 4

In this example described is a light-emitting element in which3,6-di-(dibenzothiophen-4-yl)-9-phenyl-9H-carbazole (abbreviation:DBT2PC-II, a structural formula (9)), which is a carbazole derivativerepresented by the general formula (G1), is used as a material for ahole-transport layer adjacent to a light-emitting layer using anemission center substance that emits blue fluorescence.

The molecular structures of organic compounds used in this example arerepresented by the structural formulae (iv), (vi), (viii), and (9)below. In the element structure in FIG. 1A, an electron-injection layeris provided between an electron-transport layer 114 and a secondelectrode 104.

[Fabrication of Light-Emitting Element 7]

First, a glass substrate 101 over which indium tin oxide containingsilicon (ITSO) with a thickness of 110 nm was formed as a firstelectrode 102 was prepared. The periphery of a surface of the ITSO wascovered with a polyimide film so that an area of 2 mm×2 mm of thesurface was exposed. The electrode area was 2 mm×2 mm. As a pretreatmentfor forming the light-emitting element over the substrate, the surfaceof the substrate was washed with water and baked at 200° C. for onehour, and then a UV ozone treatment was performed for 370 seconds. Then,the substrate was transferred into a vacuum evaporation apparatus whosepressure was reduced to about 10⁻⁴ Pa, vacuum baking at 170° C. for 30minutes was performed in a heating chamber of the vacuum evaporationapparatus, and then the substrate was cooled down for about 30 minutes.

Then, the substrate was fixed on a holder provided in the vacuumevaporation apparatus such that the surface of the substrate 101provided with ITSO faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, a hole-injection layer 111 was formed by co-evaporation ofDBT2PC-II represented by the above structural formula (9), which isdescribed in Embodiment 1, and molybdenum(VI) oxide such that the ratioof DBT2PC-II:molybdenum(VI) oxide was 2:1 (weight ratio). The thicknessof was the layer was set to 50 nm. Note that the co-evaporation is anevaporation method in which a plurality of different substances isconcurrently vaporized from the respective different evaporationsources.

Next, DBT2PC-II was evaporated to a thickness of 10 nm, so that thehole-transport layer 112 was formed.

Further, the light-emitting layer 113 was formed on the hole-transportlayer 112 in such a way that9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA)represented by the above structural formula (viii) andN,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenyl-pyrene-1,6-diamine(abbreviation: 1,6FLPAPm) represented by the above structural formula(vi) were evaporated to form a 30-nm-thick film so that the ratio ofCzPA to 1,6FLPAPrn was 1:0.05 (weight ratio).

Next, on the light-emitting layer 113, CzPA represented by the abovestructural formula (viii) was evaporated to a thickness of 10 nm, andthen bathophenanthroline (abbreviation: BPhen) represented by the abovestructural formula (iv) was evaporated to a thickness of 15 nm, so thatthe electron-transport layer 114 was formed. Further, lithium fluoridewas evaporated to a thickness of 1 nm on the electron-transport layer114, so that the electron-injection layer was formed. Lastly, analuminum film was formed to a thickness of 200 nm as the secondelectrode 104 functioning as a cathode, so that the light-emittingelement 7 was completed. Note that in the above evaporation processes,evaporation was all performed by a resistance heating method.

[Operation Characteristics of Light-Emitting Element 7]

The light-emitting element 7 thus obtained was sealed in a glove boxunder a nitrogen atmosphere without being exposed to the air. Then, theoperation characteristics of the light-emitting element were measured.Note that the measurements were carried out at room temperature (in anatmosphere kept at 25° C.).

FIG. 23 shows luminance versus current density characteristics of thelight-emitting element 7, FIG. 24 shows luminance versus voltagecharacteristics thereof, and FIG. 25 shows current efficiency versusluminance characteristics thereof. In FIG. 23, the vertical axisrepresents luminance (cd/m²), and the horizontal axis represents currentdensity (mA/cm²). In FIG. 24, the vertical axis represents luminance(cd/m²), and the horizontal axis represents voltage (V). In FIG. 25, thevertical axis represents current efficiency (cd/A), and the horizontalaxis represents luminance (cd/m²).

FIG. 25 reveals that the light-emitting element, in which the carbazolederivative represented by the general formula (G1) is used as a materialfor a hole-transport layer in contact with a light-emitting layer foremitting blue fluorescence, has favorable luminance versus emissionefficiency characteristics and high emission efficiency. This is becausethe carbazole derivative represented by the general formula (G1) has awide energy gap, and thus transfer of excitation energy can besuppressed despite the adjacency to a light-emitting substance thatemits blue fluorescence and has a wide energy gap. In addition, FIG. 23reveals that the light-emitting element, in which the carbazolederivative represented by the general formula (G1) is used as a materialfor a hole-transport layer adjacent to a light-emitting layer foremitting blue fluorescence, has favorable luminance versus voltagecharacteristics and can be driven with a low voltage. This indicatesthat any of the carbazole derivatives represented by the general formula(G1) has an excellent carrier-transport property.

FIG. 26 shows an emission spectrum when a current of 1 mA was made toflow in the fabricated light-emitting element 7. In FIG. 26, thehorizontal axis represents emission wavelength (nm), and the verticalaxis represents emission intensity. The emission intensity is shown as avalue relative to the greatest emission intensity assumed to be 1. FIG.26 reveals that the light-emitting element 7 emits blue light due to1,6FLPAPrn, which is the emission center substance.

Example 5

In this example described is a light-emitting element in which2,7-di-(dibenzothiophen-4-yl)-9-phenyl-9H-carbazole (abbreviation:2,7DBT2PC-II, a structural formula (10)), which is a carbazolederivative represented by the general formula (G1), is used as amaterial for a hole-transport layer adjacent to a light-emitting layerusing an emission center substance that emits blue fluorescence.

The molecular structures of organic compounds used in this example arerepresented by the structural formulae (iv), (vi), (viii), and (10)below. In the element structure in FIG. 1A, an electron-injection layeris provided between an electron-transport layer 114 and a secondelectrode 104.

[Fabrication of Light-Emitting Element 8]

First, a glass substrate 101 over which indium tin oxide containingsilicon (ITSO) with a thickness of 110 nm was formed as a firstelectrode 102 was prepared. The periphery of a surface of the ITSO wascovered with a polyimide film so that an area of 2 mm×2 mm of thesurface was exposed. The electrode area was 2 mm×2 mm. As a pretreatmentfor forming the light-emitting element over the substrate, the surfaceof the substrate was washed with water and baked at 200° C. for onehour, and then a UV ozone treatment was performed for 370 seconds. Then,the substrate was transferred into a vacuum evaporation apparatus whosepressure was reduced to about 10⁻⁴ Pa, vacuum baking at 170° C. for 30minutes was performed in a heating chamber of the vacuum evaporationapparatus, and then the substrate was cooled down for about 30 minutes.

Then, the substrate was fixed on a holder provided in the vacuumevaporation apparatus such that the surface of the substrate 101provided with ITSO faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, a hole-injection layer 111 was formed by co-evaporation of2,7DBT2PC-II represented by the above structural formula (10), which isdescribed in Embodiment 1, and molybdenum(VI) oxide such that the ratioof 2,7DBT2PC-II:molybdenum(VI) oxide was 2:1 (weight ratio). Thethickness of was the layer was set to 50 nm. Note that theco-evaporation is an evaporation method in which a plurality ofdifferent substances is concurrently vaporized from the respectivedifferent evaporation sources.

Next, 2,7DBT2PC-II was evaporated to a thickness of 10 nm, so that thehole-transport layer 112 was formed.

Further, the light-emitting layer 113 was formed on the hole-transportlayer 112 in such a way that9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA)represented by the above structural formula (viii) andN,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenyl-pyrene-1,6-diamine(abbreviation: 1,6FLPAPrn) represented by the above structural formula(vi) were evaporated to faun a 30-nm-thick film so that the ratio ofCzPA to 1,6FLPAPrn was 1:0.05 (weight ratio).

Next, on the light-emitting layer 113, Alq represented by the abovestructural formula (vii) was evaporated to a thickness of 10 nm, andthen bathophenanthroline (abbreviation: BPhen) represented by the abovestructural formula (iv) was evaporated to a thickness of 15 nm, so thatthe electron-transport layer 114 was formed. Further, lithium fluoridewas evaporated to a thickness of 1 nm on the electron-transport layer114, so that the electron-injection layer was formed. Lastly, analuminum film was formed to a thickness of 200 nm as the secondelectrode 104 functioning as a cathode, so that the light-emittingelement 8 was completed. Note that in the above evaporation processes,evaporation was all performed by a resistance heating method.

[Operation Characteristics of Light-Emitting Element 8]

The light-emitting element 8 thus obtained was sealed in a glove boxunder a nitrogen atmosphere without being exposed to the air. Then, theoperation characteristics of the light-emitting element were measured.Note that the measurements were carried out at room temperature (in anatmosphere kept at 25° C.).

FIG. 27 shows luminance versus current density characteristics of thelight-emitting element 8, FIG. 28 shows luminance versus voltagecharacteristics thereof, and FIG. 29 shows current efficiency versusluminance characteristics thereof. In FIG. 27, the vertical axisrepresents luminance (cd/m²), and the horizontal axis represents currentdensity (mA/cm²). In FIG. 28, the vertical axis represents luminance(cd/m²), and the horizontal axis represents voltage (V). In FIG. 29, thevertical axis represents current efficiency (cd/A), and the horizontalaxis represents luminance (cd/m²).

FIG. 29 reveals that the light-emitting element, in which the carbazolederivative represented by the general formula (G1) is used as a materialfor a hole-transport layer in contact with a light-emitting layer foremitting blue fluorescence, has favorable luminance versus emissionefficiency characteristics and high emission efficiency. This is becausethe carbazole derivative represented by the general formula (G1) has awide energy gap, and thus transfer of excitation energy can besuppressed despite the adjacency to a light-emitting substance thatemits blue fluorescence and has a wide energy gap. In addition, FIG. 27reveals that the light-emitting element, in which the carbazolederivative represented by the general formula (G1) is used as a materialfor a hole-transport layer adjacent to a light-emitting layer foremitting blue fluorescence, has favorable luminance versus voltagecharacteristics and can be driven with a low voltage. This indicatesthat any of the carbazole derivatives represented by the general formula(G1) has an excellent carrier-transport property.

FIG. 30 shows an emission spectrum when a current of 1 mA was made toflow in the fabricated light-emitting element 8. In FIG. 30, thehorizontal axis represents emission wavelength (nm), and the verticalaxis represents emission intensity. The emission intensity is shown as avalue relative to the greatest emission intensity assumed to be 1. FIG.30 reveals that the light-emitting element 8 emits blue light due to1,6FLPAPrn, which is the emission center substance.

Example 6 Synthesis Example 1

In this example is described a method of synthesizing2-[4-{3-(dibenzothiophen-4-yl)-9H-carbazol-9-yl}phenyl]-1-phenylbenzimidazole(abbreviation: DBTCzBIm-II), which is the carbazole derivativerepresented by the general formula (G1). A structure of DBTCzBIm-II isillustrated in the following structural formula (1).

First, a method of synthesizing 3-(dibenzothiophen-4-yl)-9H-carbazole,which is a synthetic intermediate of DBTCzBIm-II, will be described.3-(Dibenzothiophen-4-yl)-9H-carbazole is a carbazole derivativerepresented by a structural formula below. A structure of3-(dibenzothiophen-4-yl)-9H-carbazole is shown in the followingstructural formula (2).

Step 1: Synthesis of 3-(Dibenzothiophen-4-yl)-9H-carbazole

In a 200-mL three-neck flask were put 3.0 g (12 mmol) of3-bromocarbazole, 2.8 g (12 mmol) of dibenzothiophene-4-boronic acid,and 150 mg (0.5 mol) of tri(ortho-tolyl)phosphine, and the air in theflask was replaced with nitrogen. To this mixture were added 40 mL oftoluene, 40 mL of ethanol, and 15 mL (2.0 mol/L) of an aqueous potassiumcarbonate solution. In the flask, the mixture was degassed by beingstirred under reduced pressure. After the degassing, replacement withnitrogen was performed, and 23 mg (0.10 mmol) of palladium(II) acetatewas added to this mixture, and then the mixture was refluxed at 110° C.for 3 hours. After the reflux, the mixture was cooled to roomtemperature, and then the obtained solid was collected by suctionfiltration. The collected solid was dissolved in 100 mL of toluene, andthis solution was filtered through Celite (produced by Wako PureChemical Industries, Ltd., Catalog No. 531-16855), Florisil (produced byWako Pure Chemical Industries, Ltd., Catalog No. 540-00135), andalumina. The solid obtained by concentration of the obtained filtratewas recrystallized from toluene/hexane, so that 1.4 g of a white solidwas obtained in 32% yield. The synthesis scheme of Step 1 is illustratedin (a-1).

Step 2: Synthesis ofN-Phenyl-2-{4-[3-(dibenzothiophen-4-yl)-9H-carbazol-9-yl]phenyl}benzimidazole(abbreviation: DBTCzBIm-II)

In a 100-mL three-neck flask were put 0.36 g (1.0 mmol) ofN-phenyl-2-(4-bromophenyl)benzimidazole and 0.36 g (1.0 mmol) of3-(dibenzothiophen-4-yl)-9H-carbazole, and the air in the flask wasreplaced with nitrogen. To this mixture were added 10 mL of toluene,0.10 mL of tri(tert-butyl)phosphine (a 10 wt % hexane solution), 0.15 g(4.3 mmol) of sodium tert-butoxide. This mixture was degassed whilebeing stirred under reduced pressure. After this mixture was heated to80° C., 5.0 mg (0.025 mmol) of bis(dibenzylideneacetone)palladium(0) wasadded thereto, and then the mixture was stirred at 80° C. for 3 hours.After the stirring, 14 mg (0.025 mmol) ofbis(dibenzylideneacetone)palladium(0) was added to this mixture, andthen it was further stirred at 110° C. for 7.5 hours. After thestirring, about 30 mL of toluene was added to the mixture, and then itwas stirred at 80° C. This mixture was subjected to hot filtration withethyl acetate through Celite (produced by Wako Pure Chemical Industries,Ltd., Catalog No. 531-16855), Florisil (produced by Wako Pure ChemicalIndustries, Ltd., Catalog No. 540-00135), and alumina. The obtainedfiltrate was concentrated to give a white solid. The obtained solid wasdissolved in toluene. The mixture was purified by silica gel columnchromatography (a developing solvent in which the hexane/ethyl acetateratio was 4:1), and further recrystallized from toluene/hexane, so that0.41 g of a white solid was obtained in 65% yield. The synthesis schemeof Step 2 is illustrated in (b-1).

Then, 0.40 g of the obtained white solid was purified. Using a trainsublimation method, the purification was conducted by heating of thewhite solid at 290° C. under a pressure of 2.3 Pa with a flow rate ofargon gas 5.0 of mL/min. After the purification, 0.32 g of a colorlesstransparent solid was obtained in 78% yield.

The colorless and transparent solid after the purification was subjectedto nuclear magnetic resonance (¹H NMR) spectroscopy. The measurementdata are shown below. In addition, ¹H NMR charts are shown in FIGS. 31Aand 31B. Note that FIG. 31B is a chart where the range of from 7 ppm to8.75 ppm in FIG. 31A is enlarged.

¹H NMR (CDCl₃, 300 MHz): δ=7.31-7.42 (m, 4H), 7.44-7.49 (m, 6H),7.51-7.64 (m, 8H), 7.79-7.89 (m, 4H), 7.94 (d, J=7.8 Hz, 1H), 8.45-8.23(m, 3H), 8.49 (d, J=2.1 Hz, 1H)

The measurement results showed that DBTCzBIm-II, which is the carbazolederivative represented by the above structural formula (1), wasobtained.

Further, an absorption spectrum of DBTCzBIm-II in a toluene solution ofDBTCzBIm-II is shown in FIG. 32, and an absorption spectrum of a thinfilm of DBTCzBIm-II is shown in FIG. 33. An ultraviolet-visiblespectrophotometer (V-550, manufactured by JASCO Corporation) was usedfor the measurements of the absorption spectra. In the case of thetoluene solution, the measurements were made with the toluene solutionof DBTCzBIm-II put in a quartz cell, and the absorption spectrumobtained by subtraction of the absorption spectra of quartz and toluenefrom the measured spectra is shown in the drawing. In addition, as forthe absorption spectrum of the thin film, a sample was prepared byevaporation of DBTCzBIm-II on a quartz substrate, and the absorptionspectrum obtained by subtraction of that of quartz from the measuredspectra is shown in the drawing. In FIG. 32 and FIG. 33, the horizontalaxis represents wavelength (nm) and the vertical axis representsabsorption intensity (arbitrary unit).

An emission spectrum of DBTCzBIm-II in the toluene solution ofDBTCzBIm-II is shown in FIG. 34, and an emission spectrum of the thinfilm of DBTCzBIm-II is shown in FIG. 35. As in the measurements of theabsorption spectra, an ultraviolet-visible spectrophotometer (V-550,manufactured by JASCO Corporation) was used for the measurements. Theemission spectrum in the case of the toluene solution was measured withthe toluene solution of DBTCzBIm-II put in a quartz cell, and theemission spectrum of the thin film was measured with a sample preparedby evaporation of DBTCzBIm-II on a quartz substrate. FIG. 34 shows thatthe greatest emission wavelength of DBTCzBIm-II in the toluene solutionof DBTCzBIm-II was around 377 nm (at an excitation wavelength of 340 nm)and FIG. 35 shows that the greatest emission wavelength of the thin filmof DBTCzBIm-II was around 402 nm (at an excitation wavelength of 339nm).

Further, the ionization potential of DBTCzBIm-II in a thin film statewas measured by a photoelectron spectrometer (AC-2, manufactured byRiken Keiki, Co., Ltd.) in air. The obtained value of the ionizationpotential was converted to a negative value, so that the HOMO level ofDBTCzBIm-II was −5.68 eV. From the data of the absorption spectra of thethin film in FIG. 33, the absorption edge of DBTCzBIm-II, which wasobtained from Tauc plot with an assumption of direct transition, was3.31 eV. Therefore, the optical energy gap of DBTCzBIm-II in the solidstate was estimated at 3.31 eV; from the values of the HOMO levelobtained above and this energy gap, the LUMO level of DBTCzBIm-II wasable to be estimated at −2.37 eV. It was thus found that DBTCzBIm-II hada wide energy gap of 3.31 eV in the solid state.

Further, the oxidation reaction characteristics of DBTCzBIm-II weremeasured. The oxidation reaction characteristics were examined by cyclicvoltammetry (CV) measurements. Note that an electrochemical analyzer(ALS model 600A or 600C, manufactured by BAS Inc.) was used for themeasurements.

For a solution for the CV measurements, dehydrated N,N-dimethylformamide(DMF, product of Sigma-Aldrich Inc., 99.8%, catalog No. 22705-6) wasused as a solvent, and tetra-n-butylammonium perchlorate (n-Bu₄NClO₄,product of Tokyo Chemical Industry Co., Ltd., catalog No. T0836), whichwas a supporting electrolyte, was dissolved in the solvent such that theconcentration thereof was 100 mmol/L. Further, the object to be measuredwas also dissolved in the solvent such that the concentration thereofwas 2 mmol/L. A platinum electrode (a PTE platinum electrode, product ofBAS Inc.) was used as a working electrode; a platinum electrode (a VC-3Pt counter electrode (5 cm), product of BAS Inc.) was used as anauxiliary electrode; and an Ag/Ag⁺ electrode (an RE5 nonaqueous solventreference electrode, product of BAS Inc.) was used as a referenceelectrode. Note that the measurements were conducted at room temperature(20° C. to 25° C.). The scan rates for the CV measurements wereuniformly set to 0.1 V/s.

In the measurements, scanning in which the potential of the workingelectrode with respect to the reference electrode was changed from 0.00V to 1.10 V and then changed from 1.10 V to 0.00 V was one cycle, and100 cycles were performed.

The measurement results revealed that DBTCzBIm-II showed propertieseffective against repetition of redox reactions between an oxidizedstate and a neutral state without a large variation in oxidation peakeven after the 100 cycles in the measurements.

Further, the HOMO level of DBTCzBIm-II was determined also bycalculation from the CV measurement results.

First, the potential energy of the reference electrode with respect tothe vacuum level used was found to be −4.94 eV. The oxidation peakpotential E_(pa) of DBTCzBIm-II was 1.03 V. In addition, the reductionpeak potential E_(pc) thereof was 0.90 V. Therefore, a half-wavepotential (an intermediate potential between E_(pa) and E_(pc)) can becalculated at 0.97 V. This means that DBTCzBIm-II is oxidized by anelectric energy of 0.97 [V versus Ag/Ag⁺], and this energy correspondsto the HOMO level. Here, since the potential energy of the referenceelectrode, which was used in this example, with respect to the vacuumlevel is −4.94 [eV] as described above, the HOMO level of DBTCzBIm-IIwas calculated as follows: −4.94−0.97=−5.91 [eV].

Note that the potential energy of the reference electrode (Ag/Ag⁺electrode) with respect to the vacuum level corresponds to the Fermilevel of the Ag/Ag⁺ electrode, and should be calculated from a valueobtained by measuring a substance whose potential energy with respect tothe vacuum level is known, with the use of the reference electrode(Ag/Ag⁺ electrode).

How the potential energy (eV) of the reference electrode (Ag/Ag⁺electrode), which was used in this example, with respect to the vacuumlevel is determined by calculation will be specifically described. It isknown that the oxidation-reduction potential of ferrocene in methanol is+0.610 V [vs. SHE] with respect to a standard hydrogen electrode(Reference: Christian R. Goldsmith et al., J. Am. Chem. Soc., Vol. 124,No. 1, pp. 83-96, 2002). In contrast, using the reference electrode usedin this example, the oxidation-reduction potential of ferrocene inmethanol was calculated at +0.11 V [vs. Ag/Ag⁺]. Thus, it was found thatthe potential energy of the reference electrode used in this example waslower than that of the standard hydrogen electrode by 0.50 [eV].

Here, it is known that the potential energy of the standard hydrogenelectrode with respect to the vacuum level is −4.44 eV (Reference:Toshihiro Ohnishi and Tamami Koyama, High molecular EL material,Kyoritsu shuppan, pp. 64-67). Therefore, the potential energy of thereference electrode used in this example with respect to the vacuumlevel can be calculated at −4.44−0.50=−4.94 [eV].

Example 7 Synthesis Example 2

In this example is described a method of synthesizing2-[4-{3-(dibenzofuran-4-yl)-9H-carbazol-9-yl}phenyl]-1-phenylbenzimidazole(abbreviation: DBFCzBIm-II), which is one of the carbazole derivativesdescribed in Embodiment 1. A structure of DBFCzBIm-II is illustrated inthe following structural formula (3).

First, a method of synthesizing 4-(9H-carbazol-3-yl)dibenzofuran, whichis a synthetic intermediate of DBFCzBIm-II, will be described.4-(9H-Carbazol-3-yl)dibenzofuran is a carbazole derivative representedby the following structural formula (4).

Step 1: Synthesis of 4-(9H-Carbazol-3-yl)dibenzofuran

In a 200-mL three-neck flask were put 2.0 g (8.1 mmol) of3-bromocarbazole, 1.7 g (8.1 mmol) of dibenzofuran-4-boronic acid, and150 mg (0.5 mol) of tri(ortho-tolyl)phosphine, and the air in the flaskwas replaced with nitrogen. To this mixture were added 20 mL of toluene,20 mL of ethanol, and 15 mL (0.2 mol) of an aqueous potassium carbonatesolution (2.0 mol/L). In the flask, the mixture was degassed by beingstirred under reduced pressure. After 23 mg (0.10 mmol) of palladium(II)acetate was added to this mixture, the mixture was refluxed at 80° C.After the reflux, the mixture was cooled to room temperature, and thenthe obtained solid was collected by suction filtration. The collectedsolid was dissolved in 100 mL of toluene, and this solution was filteredthrough Celite (produced by Wako Pure Chemical Industries, Ltd., CatalogNo. 531-16855), alumina, and Florisil (produced by Wako Pure ChemicalIndustries, Ltd., Catalog No. 540-00135). The solid obtained byconcentration of the obtained filtrate was recrystallized fromtoluene/hexane, so that 2.3 g of a white solid was obtained in 85%yield. The synthesis scheme of Step 1 is illustrated in (a-2).

Step 2: Synthesis of2-[4-{3-(Dibenzofuran-4-yl)-9H-carbazol-9-yl}phenyl]-1-phenylbenzimidazole(abbreviation: DBFCzBIm-II)

To a 100-mL three-neck flask were added 0.70 g (1.0 mmol) of2-(4-bromophenyl)-3-phenylbenzimidazole and 0.67 g (1.0 mmol) of4-(9H-carbazol-3-yl)dibenzofuran, and the air in the flask was replacedwith nitrogen. To this mixture were added 15 mL of toluene, 0.10 mL oftri(tert-butyl)phosphine (a 10 wt % hexane solution), 0.48 g (4.3 mmol)of sodium tert-butoxide. This mixture was degassed while being stirredunder reduced pressure. This mixture was stirred at 110° C. for 20hours. After the stirring, the mixture was washed twice with about 30 mLof water, and the mixture was separated into an organic layer and anaqueous layer. Then, the aqueous layer was subjected to extraction twicewith about 30 mL of toluene. The organic layer and the solution of theextract were combined and washed once with about 100 mL of saturatedbrine. The obtained organic layer was dried over magnesium sulfate, andthis mixture was subjected to filtration through Celite (produced byWako Pure Chemical Industries, Ltd., Catalog No. 531-16855), Florisil(produced by Wako Pure Chemical Industries, Ltd., Catalog No.540-00135), and alumina. The obtained filtrate was concentrated to givea brown solid. The obtained brown solid was purified by silica gelcolumn chromatography (a developing solvent in which the ethylacetate/toluene ratio was 5:95), and further recrystallized fromhexane/toluene, so that 0.86 g of a pale brown solid was obtained in 71%yield. The synthesis scheme of Step 2 is illustrated in (b-2).

By a train sublimation method, 854 mg of the obtained pale brown solidwas purified. In the purification, the pressure was 1.8 Pa, the flowrate of argon gas was 5.0 mL/min, and the temperature of the heating was290° C. After the purification, 0.64 g of a pale brown solid of thesubstance which was the object of the synthesis was obtained in a yieldof 75%.

The pale brown solid after the purification was subjected to nuclearmagnetic resonance (¹H NMR) spectroscopy. The measurement data are shownbelow. In addition, ¹H NMR charts are shown in FIGS. 36A and 36B. Notethat FIG. 36B is a chart where the range of from 7 ppm to 9 ppm in FIG.36A is enlarged.

¹H NMR (CDCl₃, 300 MHz): δ=7.31-7.50 (m, 11H), 7.54-7.65 (m, 7H), 7.72(dd, J₁=1.5 Hz, J₂=7.5 Hz, 1H), 7.88 (d, J=8.7 Hz, 2H), 7.34-8.03 (m,4H), 8.22 (d, J=7.5 Hz, 1H), 8.63 (d, J=1.5 Hz, 1H)

The measurement results showed that DBFCzBIm-II, which is the carbazolederivative represented by the above structural formula (3), wasobtained.

Further, an absorption spectrum of DBFCzBIm-II in a toluene solution ofDBFCzBIm-II is shown in FIG. 37, and an absorption spectrum of a thinfilm of DBFCzBIm-II is shown in FIG. 38. An ultraviolet-visiblespectrophotometer (V-550, manufactured by JASCO Corporation) was usedfor the measurements of the absorption spectra. In the case of thetoluene solution, the measurements were made with the toluene solutionof DBFCzBIm-II put in a quartz cell, and the absorption spectrumobtained by subtraction of the absorption spectra of quartz and toluenefrom the measured spectra is shown in the drawing. In addition, as forthe absorption spectrum of the thin film, a sample was prepared byevaporation of DBFCzBIm-II on a quartz substrate, and the absorptionspectrum obtained by subtraction of that of quartz from the measuredspectra is shown in the drawing. In FIG. 37 and FIG. 38, the horizontalaxis represents wavelength (nm) and the vertical axis representsabsorption intensity (arbitrary unit).

An emission spectrum of DBFCzBIm-II in the toluene solution ofDBFCzBIm-II is shown in FIG. 39, and an emission spectrum of the thinfilm of DBFCzBIm-II is shown in FIG. 40. As in the measurements of theabsorption spectra, an ultraviolet-visible spectrophotometer (V-550,manufactured by JASCO Corporation) was used for the measurements. Theemission spectrum was measured with the toluene solution of DBFCzBIm-IIput in a quartz cell, and the emission spectrum of the thin film wasmeasured with a sample prepared by evaporation of DBFCzBIm-II on aquartz substrate. FIG. 39 shows that the maximum emission wavelengths ofDBFCzBIm-II in a toluene solution of DBFCzBIm-II were around 380 nm and395 nm (at an excitation wavelength of 340 nm) and FIG. 40 shows thatthe greatest emission wavelength of the thin film of DBFCzBIm-II wasaround 405 nm (at an excitation wavelength of 332 nm).

Further, the ionization potential of DBFCzBIm-II in a thin film statewas measured by a photoelectron spectrometer (AC-2, manufactured byRiken Keiki, Co., Ltd.) in air. The obtained value of the ionizationpotential was converted to a negative value, so that the HOMO level ofDBFCzBIm-II was −5.71 eV. From the data of the absorption spectra of thethin film in FIG. 38, the absorption edge of DBFCzBIm-II, which wasobtained from Tauc plot with an assumption of direct transition, was3.28 eV. Therefore, the optical energy gap of DBFCzBIm-II in the solidstate was estimated at 3.28 eV; from the values of the HOMO levelobtained above and this energy gap, the LUMO level of DBFCzBIm-II wasable to be estimated at −2.43 eV. It was thus found that DBFCzBIm-II hada wide energy gap of 3.28 eV in the solid state.

Further, the oxidation reaction characteristics of DBFCzBIm-II weremeasured. The oxidation reaction characteristics were examined by cyclicvoltammetry (CV) measurements. Note that an electrochemical analyzer(ALS model 600A or 600C, manufactured by BAS Inc.) was used for themeasurements.

For a solution for the CV measurements, dehydrated N,N-dimethylformamide(DMF, product of Sigma-Aldrich Inc., 99.8%, catalog No. 22705-6) wasused as a solvent, and tetra-n-butylammonium perchlorate (n-Bu₄NClO₄,product of Tokyo Chemical Industry Co., Ltd., catalog No. T0836), whichwas a supporting electrolyte, was dissolved in the solvent such that theconcentration thereof was 100 mmol/L. Further, the object to be measuredwas also dissolved in the solvent such that the concentration thereofwas 2 mmol/L. A platinum electrode (a PTE platinum electrode, product ofBAS Inc.) was used as a working electrode; a platinum electrode (a VC-3Pt counter electrode (5 cm), product of BAS Inc.) was used as anauxiliary electrode; and an Ag/Ag⁺ electrode (an RE5 nonaqueous solventreference electrode, product of BAS Inc.) was used as a referenceelectrode. Note that the measurements were conducted at room temperature(20° C. to 25° C.). The scan rates for the CV measurements wereuniformly set to 0.1 V/s.

In the measurements, scanning in which the potential of the workingelectrode with respect to the reference electrode was changed from 0.00V to 1.12 V and then changed from 1.12 V to 0.00 V was one cycle, and100 cycles were performed.

The measurement results revealed that DBFCzBIm-II showed propertieseffective against repetition of redox reactions between an oxidizedstate and a neutral state without a large variation in oxidation peakeven after the 100 cycles in the measurements.

Further, the HOMO level of DBFCzBIm-II was determined also bycalculation from the CV measurement results.

First, the potential energy of the reference electrode with respect tothe vacuum level used was found to be −4.94 eV, as determined in Example6. The oxidation peak potential E_(pa) of DBFCzBIm-II was 1.04 V. Inaddition, the reduction peak potential E_(pc) was 0.89 V. Therefore, ahalf-wave potential (an intermediate potential between E_(pa) andE_(pc)) can be calculated at 0.97 V. This means that DBFCzBIm-II isoxidized by an electric energy of 0.97 [V versus Ag/Ag⁺], and thisenergy corresponds to the HOMO level. Here, since the potential energyof the reference electrode, which was used in this example, with respectto the vacuum level is −4.94 [eV] as described above, the HOMO level ofDBFCzBIm-II was calculated as follows: −4.94−0.97=−5.91 [eV].

Example 8 Synthesis Example 3

In this example is described a method of synthesizing3-(dibenzothiophen-4-yl)-9-(triphenylen-2-yl)-9H-carbazole(abbreviation: DBTCzTp-II), which is one of the carbazole derivativesdescribed in Embodiment 1. A structure of DBTCzTp-II is illustrated inthe following structural formula (5).

Step 1: Synthesis of 3-(Dibenzothiophen-4-yl)-9H-carbazole

This was synthesized as in Step 1 in Synthesis Example 1.

Step 2: Synthesis of DBTCzTp-II

In a 100-mL three-neck flask were put 1.0 g (2.9 mmol) of2-bromotriphenylene and 0.88 g (2.9 mmol) of3-(dibenzothiophen-4-yl)-9H-carbazole, and the air in the flask wasreplaced with nitrogen. To this mixture were added 15 mL of toluene,0.10 mL of tri(tert-butyl)phosphine (a 10 wt % hexane solution), 0.45 g(4.3 mmol) of sodium tert-butoxide. This mixture was degassed whilebeing stirred under reduced pressure. After the degassing, replacementwith nitrogen was performed, this mixture was heated to 80° C., and then14 mg (0.025 mmol) of bis(dibenzylideneacetone)palladium(0) was addedthereto. This mixture was stirred at 80° C. for 4 hours. After thestirring, 15 mg (0.025 mmol) of bis(dibenzylideneacetone)palladium(0)was added to this mixture, and then it was further stirred at 110° C.for 8 hours. After the stirring, about 30 mL of toluene was added to themixture, and then it was stirred at 80° C. The mixture was subjected tohot filtration through Celite (produced by Wako Pure ChemicalIndustries, Ltd., Catalog No. 531-16855), Florisil (produced by WakoPure Chemical Industries, Ltd., Catalog No. 540-00135), and alumina. Theobtained filtrate was concentrated to give a white solid. The obtainedsolid was dissolved in toluene. The mixture was purified by silica gelcolumn chromatography (a developing solvent in which the hexane/ethylacetate ratio was 9:1), and further recrystallized from toluene/hexane,so that 500 mg of a white solid was obtained in 27% yield. The synthesisscheme of Step 2 is illustrated in (b-3).

By a train sublimation method, 0.50 g of the obtained white solid waspurified. In the purification, the pressure was 2.1 Pa, the flow rate ofargon gas was 5.0 mL/min, and the temperature of the heating was 310° C.After the purification, 0.40 g of a colorless transparent solid wasobtained in a yield of 78%.

The colorless and transparent solid after the purification was subjectedto nuclear magnetic resonance (¹H NMR) spectroscopy. The measurementdata are shown below. In addition, ¹H NMR charts are shown in FIGS. 41Aand 41B.

¹H NMR (CDCl₃, 300 MHz): δ=7.37-7.41 (m, 2H), 7.45-7.52 (m, 3H),7.58-7.77 (m, 8H), 7.93 (dd, J₁=2.1 Hz, J₁=8.7 Hz, 1H), 7.96 (dd, J₁=1.5Hz, J₁=7.8 Hz, 1H), 8.03 (dd, J₁=1.5 Hz, J₁=8.2 Hz, 1H), 8.31 (d, J=7.5Hz, 1H), 8.61 (dd, J₁=1.5 Hz, J₂=8.0 Hz 1H), 8.72-8.77 (m, 4H),8.91-8.94 (m, 2H)

The measurement results showed that DBTCzTp-II, which is the carbazolederivative represented by the above structural formula (5), wasobtained.

Further, an absorption spectrum of DBTCzTp-II in a toluene solution ofDBTCzTp-II is shown in FIG. 42, and an absorption spectrum of a thinfilm is shown in FIG. 43. An ultraviolet-visible spectrophotometer(V-550, manufactured by JASCO Corporation) was used for the measurementsof the absorption spectra. In the case of the toluene solution, themeasurements were made with the toluene solution of DBTCzTp-II put in aquartz cell, and the absorption spectrum obtained by subtraction of theabsorption spectra of quartz and toluene from the measured spectra isshown in the drawing. In addition, as for the absorption spectrum of thethin film, a sample was prepared by evaporation of DBTCzTp-II on aquartz substrate, and the absorption spectrum obtained by subtraction ofthat of quartz from the measured spectra is shown in the drawing. InFIG. 42 and FIG. 43, the horizontal axis represents wavelength (nm) andthe vertical axis represents absorption intensity (arbitrary unit).

An emission spectrum of DBTCzTp-II in the toluene solution of DBTCzTp-IIis shown in FIG. 44, and an emission spectrum of a thin film ofDBTCzTp-II is shown in FIG. 45. As in the measurements of the absorptionspectra, an ultraviolet-visible spectrophotometer (V-550, manufacturedby JASCO Corporation) was used for the measurements. The emissionspectrum was measured with the toluene solution of DBTCzTp-II put in aquartz cell, and the emission spectrum of the thin film was measuredwith a sample prepared by evaporation of DBTCzTp-II on a quartzsubstrate. FIG. 44 shows that the maximum emission wavelengths ofDBTCzTp-II in the toluene solution of DBTCzTp-II were around 363 nm and379 nm (at an excitation wavelength of 340 nm) and FIG. 45 shows thatthe greatest emission wavelength of the thin film of DBTCzTp-II wasaround 390 nm (at an excitation wavelength of 336 nm).

Further, the ionization potential of DBTCzTp-II in a thin film state wasmeasured by a photoelectron spectrometer (AC-2, manufactured by RikenKeiki, Co., Ltd.) in air. The obtained value of the ionization potentialwas converted to a negative value, so that the HOMO level of DBTCzTp-IIwas −5.84 eV. From the data of the absorption spectra of the thin filmin FIG. 43, the absorption edge of DBTCzTp-II, which was obtained fromTauc plot with an assumption of direct transition, was 3.34 eV.Therefore, the optical energy gap of DBTCzTp-II in the solid state wasestimated at 3.34 eV; from the values of the HOMO level obtained aboveand this energy gap, the LUMO level of DBTCzTp-II was able to beestimated at −2.50 eV. It was thus found that DBTCzTp-II had a wideenergy gap of 3.34 eV in the solid state.

Further, the oxidation reaction characteristics of DBTCzTp-II weremeasured. The oxidation reaction characteristics were examined by cyclicvoltammetry (CV) measurements. Note that an electrochemical analyzer(ALS model 600A or 600C, manufactured by BAS Inc.) was used for themeasurements.

For a solution for the CV measurements, dehydrated N,N-dimethylformamide(DMF, product of Sigma-Aldrich Inc., 99.8%, catalog No. 22705-6) wasused as a solvent, and tetra-n-butylammonium perchlorate (n-Bu₄NClO₄,product of Tokyo Chemical Industry Co., Ltd., catalog No. T0836), whichwas a supporting electrolyte, was dissolved in the solvent such that theconcentration thereof was 100 mmol/L. Further, the object to be measuredwas also dissolved in the solvent such that the concentration thereofwas 2 mmol/L. A platinum electrode (a PTE platinum electrode, product ofBAS Inc.) was used as a working electrode; a platinum electrode (a VC-3Pt counter electrode (5 cm), product of BAS Inc.) was used as anauxiliary electrode; and an Ag/Ag⁺ electrode (an RE5 nonaqueous solventreference electrode, product of BAS Inc.) was used as a referenceelectrode. Note that the measurements were conducted at room temperature(20° C. to 25° C.). The scan rates for the CV measurements wereuniformly set to 0.1 V/s.

In the measurements, scanning in which the potential of the workingelectrode with respect to the reference electrode was changed from −0.05V to 1.10 V and then changed from 1.10 V to −0.05 V was one cycle, and100 cycles were performed.

The measurement results revealed that DBTCzTp-II showed propertieseffective against repetition of redox reactions between an oxidizedstate and a neutral state without a large variation in oxidation peakeven after the 100 cycles in the measurements.

Further, the HOMO level of DBTCzTp-II was determined also by calculationfrom the CV measurement results.

First, the potential energy of the reference electrode with respect tothe vacuum level used was found to be −4.94 eV, as determined in Example6. The oxidation peak potential E_(pa) of DBTCzTp-II was 1.01 V. Inaddition, the reduction peak potential E_(pc) thereof was 0.86 V.Therefore, a half-wave potential (an intermediate potential betweenE_(pa) and E_(pc)) can be calculated at 0.94 V. This means thatDBTCzTp-II is oxidized by an electric energy of 0.94 [V versus Ag/Ag⁺],and this energy corresponds to the HOMO level. Here, since the potentialenergy of the reference electrode, which was used in this example, withrespect to the vacuum level is −4.94 [eV] as described above, the HOMOlevel of DBTCzTp-II was calculated as follows: −4.94−0.94=−5.88 [eV].

Example 9 Synthesis Example 4

In this example is described a method of synthesizing3-(dibenzofuran-4-yl)-9-(triphenylen-2-yl)-9H-carbazole (abbreviation:DBFCzTp-II), which is one of the carbazole derivatives described inEmbodiment 1. A structure of DBFCzTp-II is illustrated in the followingstructural formula (6).

Step 1: Synthesis of 4-(9H-Carbazol-3-yl)dibenzofuran

This was synthesized as in Step 1 in Example 2.

Step 2: Synthesis of DBFCzTp-II

In a 50-mL three-neck flask were put 0.62 g (2.0 mmol) of2-bromotriphenylene and 0.67 g (2.0 mmol) of4-(9H-carbazol-3-yl)dibenzofuran, and the air in the flask was replacedwith nitrogen. To this mixture were added 15 mL of toluene, 0.10 mL oftri(tert-butyl)phosphine (a 10 wt % hexane solution), 0.48 g (4.3 mmol)of sodium tert-butoxide. This mixture was degassed while being stirredunder reduced pressure. After this mixture was heated at 80° C., 14 mg(0.025 mmol) of bis(dibenzylideneacetone)palladium(0) was added thereto.This mixture was stirred at 110° C. for 15.5 hours. After the stirring,the mixture was washed twice with about 30 mL of water, and the mixturewas separated into an organic layer and an aqueous layer that wassubjected to extraction. Then, the aqueous layer was subjected toextraction twice with about 30 mL of toluene. The organic layer and thesolution of the extract were combined and washed once with about 100 mLof saturated brine, and the mixture was separated into an organic layerand an aqueous layer. The obtained organic layer was dried overmagnesium sulfate, and this mixture was subjected to filtration throughCelite (produced by Wako Pure Chemical Industries, Ltd., Catalog No.531-16855), Florisil (produced by Wako Pure Chemical Industries, Ltd.,Catalog No. 540-00135), and alumina. The obtained filtrate wasconcentrated to give a brown solid. The obtained brown solid waspurified by silica gel column chromatography (a developing solvent inwhich the hexane/toluene was 2:1), and further recrystallized fromhexane/toluene, so that 0.73 g of a white solid was obtained in 65%yield. The synthesis scheme of Step 2 is illustrated in (b-4).

By a train sublimation method, 0.73 g of the obtained white solid waspurified. In the purification, the pressure was 2.2 Pa, the flow rate ofargon gas was 5.0 mL/min, and the temperature of the heating was 310° C.After the purification, 0.59 g of a colorless transparent solid wasobtained in a yield of 81%.

The colorless and transparent solid after the purification was subjectedto nuclear magnetic resonance (¹H NMR) spectroscopy. The measurementdata are shown below. In addition, ¹H NMR charts are shown in FIGS. 46Aand 46B. Note that FIG. 46B is a chart where the range of from 7.25 ppmto 9 ppm in FIG. 46A is enlarged.

¹H NMR (CDCl₃, 300 MHz): δ=7.37-7.41 (m, 2H), 7.45-7.52 (m, 3H),7.58-7.77 (m, 8H), 7.93 (dd, J₁=2.1 Hz, J₁=8.7 Hz, 1H), 7.96 (dd, J₁=1.5Hz, J₁=7.8 Hz, 1H), 8.03 (dd, J₁=1.5 Hz, J₁=8.2 Hz, 1H), 8.31 (d, J=7.5Hz, 1H), 8.61 (dd, J₁=1.5 Hz, J₂=8.0 Hz 1H), 8.72-8.77 (m, 4H),8.91-8.94 (m, 2H)

The measurement results showed that DBFCzTp-II, which is the carbazolederivative represented by the above structural formula (6), wasobtained.

Further, an absorption spectrum of DBFCzTp-II in a toluene solution ofDBFCzTp-II is shown in FIG. 47, and an absorption spectrum of a thinfilm of DBFCzTp-II is shown in FIG. 48. An ultraviolet-visiblespectrophotometer (V-550, manufactured by JASCO Corporation) was usedfor the measurements of the absorption spectra. In the case of thetoluene solution, the measurements were made with the toluene solutionof DBFCzTp-II put in a quartz cell, and the absorption spectrum obtainedby subtraction of the absorption spectra of quartz and toluene from themeasured spectra is shown in the drawing. In addition, as for theabsorption spectrum of the thin film, a sample was prepared byevaporation of DBFCzTp-II on a quartz substrate, and the absorptionspectrum obtained by subtraction of that of quartz from the measuredspectra is shown in the drawing. In FIG. 47 and FIG. 48, the horizontalaxis represents wavelength (nm) and the vertical axis representsabsorption intensity (arbitrary unit).

An emission spectrum of DBFCzTp-II in the toluene solution of DBFCzTp-IIis shown in FIG. 49, and an emission spectrum of a thin film is shown inFIG. 50. As in the measurements of the absorption spectra, anultraviolet-visible spectrophotometer (V-550, manufactured by JASCOCorporation) was used for the measurements. The emission spectrum wasmeasured with the toluene solution of DBFCzTp-II put in a quartz cell,and the emission spectrum of the thin film was measured with a sampleprepared by evaporation of DBFCzTp-II on a quartz substrate. FIG. 49shows that the maximum emission wavelengths of DBFCzTp-II in the toluenesolution of DBFCzTp-II were around 380 nm and 395 nm (at an excitationwavelength of 340 nm) and FIG. 50 shows that the greatest emissionwavelength of the thin film of DBFCzTp-II was around 413 nm (at anexcitation wavelength of 334 nm).

Further, the ionization potential of DBFCzTp-II in a thin film state wasmeasured by a photoelectron spectrometer (AC-2, manufactured by RikenKeiki, Co., Ltd.) in air. The obtained value of the ionization potentialwas converted to a negative value, so that the HOMO level of DBFCzTp-IIwas −5.79 eV. From the data of the absorption spectra of the thin filmin FIG. 48, the absorption edge of DBFCzTp-II, which was obtained fromTauc plot with an assumption of direct transition, was 3.33 eV.Therefore, the optical energy gap of DBFCzTp-II in the solid state wasestimated at 3.33 eV; from the values of the HOMO level obtained aboveand this energy gap, the LUMO level of DBFCzTp-II was able to beestimated at −2.46 eV. It was thus found that DBFCzTp-II had a wideenergy gap of 3.33 eV in the solid state.

Further, the oxidation reaction characteristics of DBFCzTp-II weremeasured. The oxidation reaction characteristics were examined by cyclicvoltammetry (CV) measurements. Note that an electrochemical analyzer(ALS model 600A or 600C, manufactured by BAS Inc.) was used for themeasurements.

For a solution for the CV measurements, dehydrated N,N-dimethylformamide(DMF, product of Sigma-Aldrich Inc., 99.8%, catalog No. 22705-6) wasused as a solvent, and tetra-n-butylammonium perchlorate (n-Bu₄NClO₄,product of Tokyo Chemical Industry Co., Ltd., catalog No. T0836), whichwas a supporting electrolyte, was dissolved in the solvent such that theconcentration thereof was 100 mmol/L. Further, the object to be measuredwas also dissolved in the solvent such that the concentration thereofwas 2 mmol/L. A platinum electrode (a PTE platinum electrode, product ofBAS Inc.) was used as a working electrode; a platinum electrode (a VC-3Pt counter electrode (5 cm), product of BAS Inc.) was used as anauxiliary electrode; and an Ag/Ag⁺ electrode (an RE5 nonaqueous solventreference electrode, product of BAS Inc.) was used as a referenceelectrode. Note that the measurements were conducted at room temperature(20° C. to 25° C.). The scan rates for the CV measurements wereuniformly set to 0.1 V/s.

In the measurements, scanning in which the potential of the workingelectrode with respect to the reference electrode was changed from 0.00V to 1.10 V and then changed from 1.10 V to 0.00 V was one cycle, and100 cycles were performed.

The measurement results revealed that DBFCzTp-II showed propertieseffective against repetition of redox reactions between an oxidizedstate and a neutral state without a large variation in oxidation peakeven after the 100 cycles in the measurements.

Further, the HOMO level of DBFCzTp-II was determined also by calculationfrom the CV measurement results.

First, the potential energy of the reference electrode with respect tothe vacuum level used was found to be −4.94 eV, as determined in Example6. The oxidation peak potential E_(pa) was 1.00 V. In addition, thereduction peak potential E_(pc) was 0.83 V. Therefore, a half-wavepotential (an intermediate potential between E_(pa) and E_(pc)) can becalculated at 0.92 V. This means that DBFCzTp-II is oxidized by anelectric energy of 0.92 [V versus Ag/Ag⁺], and this energy correspondsto the HOMO level. Here, since the potential energy of the referenceelectrode, which was used in this example, with respect to the vacuumlevel is −4.94 [eV] as described above, the HOMO level of DBFCzTp-II wascalculated as follows: −4.94−0.92=−5.86 [eV].

Example 10 Synthesis Example 5

In this example is described a method of synthesizing3-(dibenzothiophen-4-yl)-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: DBTCzPA-II), which is one of the carbazole derivativesdescribed in Embodiment 1. A structure of DBTCzPA-II is illustrated inthe following structural formula (7).

Step 1: Synthesis of 3-(Dibenzothiophen-4-yl)-9H-carbazole

This was synthesized as in Step 1 in Synthesis Example 1.

Step 2: Synthesis of DBTCzPA-II

To a 100-mL three-neck flask were added 1.8 g (4.4 mmol) of9-(4-bromophenyl)-10-phenylanthracene, 1.5 g (4.4 mmol) of3-(dibenzothiophen-4-yl)-9H-carbazole, and 0.85 g (8.8 mmol) of sodiumtert-butoxide. After the air in the flask was replaced with nitrogen, tothis mixture were added 25 mL of toluene and 2.2 mL oftri(tert-butyl)phosphine (a 10 wt % hexane solution). This mixture wasdegassed by being stirred while the pressure was reduced. After thedegassing, 0.12 g (0.22 mmol) of bis(dibenzylideneacetone)palladium(0)was added to the mixture. This mixture was stirred at 110° C. for 18hours under a nitrogen stream, so that a solid was precipitated. Afterthe stirring, this mixture was cooled to room temperature, and theobtained solid was collected by suction filtration. The collected solidwas dissolved in about 60 mL of toluene, and the obtained solution wassuction-filtered through Celite, alumina, and Florisil. The obtainedfiltrate was concentrated to give a solid and the solid wasrecrystallized from toluene, so that 1.1 g of a white powder wasobtained in 36% yield. The synthesis scheme of Step 2 is illustrated in(b-6).

Then, 1.1 g of the obtained white powder was purified. Using a trainsublimation method, the purification was conducted by heating of thewhite powder at 300° C. under a pressure of 3.0 Pa with a flow rate ofargon gas of 4.0 mL/min. After the purification, 1.0 g of a pale yellowsolid was obtained in 90% yield.

The pale yellow solid after the above purification was subjected tonuclear magnetic resonance (¹H NMR) spectroscopy. The measurement dataare shown below.

¹H NMR (CDCl₃, 300 MHz): δ=7.36-7.68 (m, 15H), 7.72-7.93 (m, 12H),8.19-8.286 (m, 3H), 8.57 (sd, J₁=1.5 Hz, 1H).

Further, a ¹H NMR chart is shown in FIG. 51. The measurement resultsshowed that DBTCzPA-II, which is the carbazole derivative represented bythe above structural formula (7), was obtained.

Further, an absorption spectrum of DBTCzPA-II in a toluene solution ofDBTCzPA-II is shown in FIG. 52, and an absorption spectrum of a thinfilm of DBTCzPA-II is shown in FIG. 53. An ultraviolet-visiblespectrophotometer (V-550, manufactured by JASCO Corporation) was usedfor the measurements of the absorption spectra. In the case of thetoluene solution, the measurements were made with the toluene solutionof DBTCzPA-II put in a quartz cell, and the absorption spectrum obtainedby subtraction of the absorption spectra of quartz and toluene from themeasured spectra is shown in the drawing. In addition, as for theabsorption spectrum of the thin film, a sample was prepared byevaporation of DBTCzPA-II on a quartz substrate, and the absorptionspectrum obtained by subtraction of that of quartz from the measuredspectra is shown in the drawing. In FIG. 52 and FIG. 53, the horizontalaxis represents wavelength (nm) and the vertical axis representsabsorption intensity (arbitrary unit).

An emission spectrum of DBTCzPA-II in the toluene solution of DBTCzPA-IIis shown in FIG. 54, and an emission spectrum of a thin film is shown inFIG. 55. As in the measurements of the absorption spectra, anultraviolet-visible spectrophotometer (V-550, manufactured by JASCOCorporation) was used for the measurements. The emission spectrum wasmeasured with the toluene solution of DBTCzPA-II put in a quartz cell,and the emission spectrum of the thin film was measured with a sampleprepared by evaporation of DBTCzPA-II on a quartz substrate. FIG. 54shows that the greatest emission wavelength of DBTCzPA-II in the toluenesolution of DBTCzPA-II was around 436 nm (at an excitation wavelength of376 nm) and FIG. 55 shows that the greatest emission wavelength of thethin film of DBTCzPA-II was around 447 nm (at an excitation wavelengthof 400 nm).

Further, the ionization potential of DBTCzPA-II in a thin film state wasmeasured by a photoelectron spectrometer (AC-2, manufactured by RikenKeiki, Co., Ltd.) in air. The obtained value of the ionization potentialwas converted to a negative value, so that the HOMO level of DBTCzPA-IIwas −5.73 eV. From the data of the absorption spectra of the thin filmin FIG. 53, the absorption edge of DBTCzPA-II, which was obtained fromTauc plot with an assumption of direct transition, was 2.92 eV.Therefore, the optical energy gap of DBTCzPA-II in the solid state wasestimated at 2.92 eV; from the values of the HOMO level obtained aboveand this energy gap, the LUMO level of DBTCzPA-II was able to beestimated at −2.81 eV. It was thus found that DBTCzPA-II had a wideenergy gap of 2.92 eV in the solid state.

Further, the oxidation reaction characteristics of DBTCzPA-II weremeasured. The oxidation reaction characteristics were examined by cyclicvoltammetry (CV) measurements. Note that an electrochemical analyzer(ALS model 600A or 600C, manufactured by BAS Inc.) was used for themeasurements.

For a solution for the CV measurements, dehydrated N,N-dimethylformamide(DMF, product of Sigma-Aldrich Inc., 99.8%, catalog No. 22705-6) wasused as a solvent, and tetra-n-butylammonium perchlorate (n-Bu₄NClO₄,product of Tokyo Chemical Industry Co., Ltd., catalog No. T0836), whichwas a supporting electrolyte, was dissolved in the solvent such that theconcentration thereof was 100 mmol/L. Further, the object to be measuredwas also dissolved in the solvent such that the concentration thereofwas 2 mmol/L. A platinum electrode (a PTE platinum electrode, product ofBAS Inc.) was used as a working electrode; a platinum electrode (a VC-3Pt counter electrode (5 cm), product of BAS Inc.) was used as anauxiliary electrode; and an Ag/Ag⁺ electrode (an RE5 nonaqueous solventreference electrode, product of BAS Inc.) was used as a referenceelectrode. Note that the measurements were conducted at room temperature(20° C. to 25° C.). The scan rates for the CV measurements wereuniformly set to 0.1 V/s.

In the measurements, scanning in which the potential of the workingelectrode with respect to the reference electrode was changed from −0.05V to 1.10 V and then changed from 1.1 V to −0.05 V was one cycle, and100 cycles were performed.

The measurement results revealed that DBTCzPA-II showed propertieseffective against repetition of redox reactions between an oxidizedstate and a neutral state without a large variation in oxidation peakeven after the 100 cycles in the measurements.

Further, the HOMO level of DBTCzPA-II was determined also by calculationfrom the CV measurement results.

First, the potential energy of the reference electrode with respect tothe vacuum level used was found to be −4.94 eV, as determined in Example6. The oxidation peak potential E_(pa) of DBTCzPA-II was 1.01 V. Inaddition, the reduction peak potential E_(pc) thereof was 0.86 V.Therefore, a half-wave potential (an intermediate potential betweenE_(pa) and E_(pc)) can be calculated at 0.94 V. This means thatDBTCzPA-II is oxidized by an electric energy of 0.94 [V versus Ag/Ag⁺],and this energy corresponds to the HOMO level. Here, since the potentialenergy of the reference electrode, which was used in this example, withrespect to the vacuum level is −4.94 [eV] as described above, the HOMOlevel of DBTCzPA-II was calculated as follows: −4.94−0.94=−5.88 [eV].

Example 11 Synthesis Example 6

In this example is described a method of synthesizing3-(dibenzofuran-4-yl)-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: DBFCzPA-II), which is one of the carbazole derivativesdescribed in Embodiment 1. A structure of DBFCzPA-II is illustrated inthe following structural formula (8).

Step 1: Synthesis of 3-(Dibenzofuran-4-yl)-9H-carbazole

This was synthesized as in Step 1 in Synthesis Example 2.

Step 2: Synthesis of DBFCzPA-II

To a 50-mL three-neck flask were added 0.61 g (1.5 mmol) of9-(4-bromophenyl)-10-phenylanthracene, 0.50 g (1.5 mmol) of3-(dibenzofuran-4-yl)-9H-carbazole, and 0.29 g (3.0 mmol) of sodiumtert-butoxide. After the air in the flask was replaced with nitrogen, tothis mixture were added 8.0 mL of toluene and 0.76 mL oftri(tert-butyl)phosphine (a 10 wt % hexane solution). This mixture wasdegassed by being stirred while the pressure was reduced. After thedegassing, 43 mg (0.075 mmol) of bis(dibenzylideneacetone)palladium(0)was added to the mixture. This mixture was stirred at 110° C. for 10hours under a nitrogen stream. After the stirring, the obtained mixturewas suction-filtered through Celite (produced by Wako Pure ChemicalIndustries, Ltd., Catalog No. 531-16855), Florisil (produced by WakoPure Chemical Industries, Ltd., Catalog No. 540-00135), and alumina. Theobtained filtrate was concentrated to give an oily substance. Theobtained oily substance was purified by silica gel column chromatography(a developing solvent in which the hexane/toluene ratio was 5:1), andthe obtained solid was recrystallized from toluene/hexane, so that 0.63g of a white powder was obtained in 63% yield. The synthesis scheme ofStep 2 is illustrated in (b-6).

Then, 0.63 g of the obtained white powder was purified. Using a trainsublimation method, the purification was conducted by heating of thewhite powder at 300° C. under a pressure of 3.0 Pa with a flow rate ofargon gas of 4.0 mL/min. After the purification, 0.55 g of a pale yellowsolid was obtained in 87% yield.

The pale yellow solid after the above purification was subjected tonuclear magnetic resonance (¹H NMR) spectroscopy. The measurement dataare shown below.

¹H NMR(CDCl₃, 300 M Hz): δ=7.30-7.66 (m, 15H), 7.71-7.79 (m, 6H),7.83-7.91 (m, 5H), 7.97 (dd, J₁=1.2 Hz, J₂=7.2 Hz, 1H), 8.04 (dd,J₁=0.90 Hz, J₂=7.8 Hz, 1H), 8.10 (dd, J₁=1.8 Hz, J₂=8.4 Hz, 1H), 8.31(d, J₁=7.5 Hz, 1H), 8.72 (sd, J₁=0.90 Hz, 1H).

Further, a ¹H NMR chart is shown in FIG. 56. The measurement resultsshowed that DBFCzPA-II, which is the carbazole derivative represented bythe above structural formula (8), was obtained.

Further, an absorption spectrum of DBFCzPA-II in a toluene solution ofDBFCzPA-II is shown in FIG. 57, and an absorption spectrum of a thinfilm of DBFCzPA-II is shown in FIG. 58. An ultraviolet-visiblespectrophotometer (V-550, manufactured by JASCO Corporation) was usedfor the measurements of the absorption spectra. In the case of thetoluene solution, the measurements were made with the toluene solutionof DBFCzPA-II put in a quartz cell, and the absorption spectrum obtainedby subtraction of the absorption spectra of quartz and toluene from themeasured spectra is shown in the drawing. In addition, as for theabsorption spectrum of the thin film, a sample was prepared byevaporation of DBFCzPA-II on a quartz substrate, and the absorptionspectrum obtained by subtraction of that of quartz from the measuredspectra is shown in the drawing. In FIG. 57 and FIG. 58, the horizontalaxis represents wavelength (nm) and the vertical axis representsabsorption intensity (arbitrary unit).

An emission spectrum of DBFCzPA-II in the toluene solution of DBFCzPA-IIis shown in FIG. 59, and an emission spectrum of a thin film is shown inFIG. 60. As in the measurements of the absorption spectra, anultraviolet-visible spectrophotometer (V-550, manufactured by JASCOCorporation) was used for the measurements. The emission spectrum wasmeasured with the toluene solution of DBFCzPA-II put in a quartz cell,and the emission spectrum of the thin film was measured with a sampleprepared by evaporation of DBFCzPA-II on a quartz substrate. FIG. 59shows that the greatest emission wavelength of DBFCzPA-II in the toluenesolution of DBFCzPA-II was around 435 nm (at an excitation wavelength of376 nm) and FIG. 60 shows that the greatest emission wavelength of thethin film of DBFCzPA-II was around 449 nm (at an excitation wavelengthof 380 nm).

Further, the ionization potential of DBFCzPA-II in a thin film state wasmeasured by a photoelectron spectrometer (AC-2, manufactured by RikenKeiki, Co., Ltd.) in air. The obtained value of the ionization potentialwas converted to a negative value, so that the HOMO level of DBFCzPA-IIwas −5.64 eV. From the data of the absorption spectra of the thin filmin FIG. 58, the absorption edge of DBFCzPA-II, which was obtained fromTauc plot with an assumption of direct transition, was 2.93 eV.Therefore, the optical energy gap of DBFCzPA-II in the solid state wasestimated at 2.93 eV; from the values of the HOMO level obtained aboveand this energy gap, the LUMO level of DBFCzPA-II was able to beestimated at −2.71 eV. It was thus found that DBFCzPA-II had a wideenergy gap of 2.93 eV in the solid state.

Further, the oxidation reaction characteristics of DBFCzPA-II weremeasured. The oxidation reaction characteristics were examined by cyclicvoltammetry (CV) measurements. Note that an electrochemical analyzer(ALS model 600A or 600C, manufactured by BAS Inc.) was used for themeasurements.

For a solution for the CV measurements, dehydrated N,N-dimethylformamide(DMF, product of Sigma-Aldrich Inc., 99.8%, catalog No. 22705-6) wasused as a solvent, and tetra-n-butylammonium perchlorate (n-Bu₄NClO₄,product of Tokyo Chemical Industry Co., Ltd., catalog No. T0836), whichwas a supporting electrolyte, was dissolved in the solvent such that theconcentration thereof was 100 mmol/L. Further, the object to be measuredwas also dissolved in the solvent such that the concentration thereofwas 2 mmol/L. A platinum electrode (a PTE platinum electrode, product ofBAS Inc.) was used as a working electrode; a platinum electrode (a VC-3Pt counter electrode (5 cm), product of BAS Inc.) was used as anauxiliary electrode; and an Ag/Ag⁺ electrode (an RE5 nonaqueous solventreference electrode, product of BAS Inc.) was used as a referenceelectrode. Note that the measurements were conducted at room temperature(20° C. to 25° C.). The scan rates for the CV measurements wereuniformly set to 0.1 V/s.

In the measurements, scanning in which the potential of the workingelectrode with respect to the reference electrode was changed from 0.35V to 0.95 V and then changed from 0.95 V to 0.35 V was one cycle, and100 cycles were performed.

The measurement results revealed that DBFCzPA-II showed propertieseffective against repetition of redox reactions between an oxidizedstate and a neutral state without a large variation in oxidation peakeven after the 100 cycles in the measurements.

Further, the HOMO level of DBFCzPA-II was determined also by calculationfrom the CV measurement results.

First, the potential energy of the reference electrode with respect tothe vacuum level used was found to be −4.94 eV, as determined in Example6. The oxidation peak potential E_(pa) of DBFCzPA-II was 0.91 V. Inaddition, the reduction peak potential E_(pc) thereof was 0.78 V.Therefore, a half-wave potential (an intermediate potential betweenE_(pa) and E_(pc)) can be calculated at 0.85 V. This means thatDBFCzPA-II is oxidized by an electric energy of 0.85 [V versus Ag/Ag⁺],and this energy corresponds to the HOMO level. Here, since the potentialenergy of the reference electrode, which was used in this example, withrespect to the vacuum level is −4.94 [eV] as described above, the HOMOlevel of DBFCzPA-II was calculated as follows: −4.94−0.85=−5.79 [eV].

Example 12 Synthesis Example 7

In this example is described a method of synthesizing3,6-di-(dibenzothiophen-4-yl)-9-phenyl-9H-carbazole (abbreviation:DBT2PC-II), which is one of the carbazole derivatives described inEmbodiment 1. A structure of DBT2PC-II is illustrated in the followingstructural formula (9).

Step 1: Synthesis of 3,6-Di-(dibenzothiophen-4-yl)-9-phenyl-9H-carbazole(abbreviation: DBT2PC-II)

To a 200-mL three-neck flask were added 2.0 g (5.0 mmol) of3,6-dibromo-9-phenyl-9H-carbazole, 3.2 g (11 mmol) ofdibenzothiophene-4-boronic acid, 10 mg (0.1 mmol) of palladium(II)acetate, 30 mg (0.1 mmol) of tri(ortho-tolyl)phosphine, 50 mL oftoluene, 5 mL of ethanol, and 7.5 mL of a 2 mol/L aqueous potassiumcarbonate solution. This mixture was degassed while being stirred underreduced pressure, and then heated and stirred at 90° C. for 6 hours in anitrogen atmosphere to be reacted. After the reaction, this reactionmixture solution was cooled to room temperature, and then filtered togive a residue while being washed with water, ethanol, toluene, andhexane in this order. The residue was purified by silica gel columnchromatography (a developing solvent in which the toluene/hexane ratiowas 1:3). The fraction thus obtained was concentrated, acetone andethanol were added thereto, and the mixture was irradiated withultrasonic waves. Then, recrystallization gave 1.4 g of a white powderin 47% yield. The synthesis scheme of Step 1 is illustrated in (C-7).

The obtained white powder was subjected to nuclear magnetic resonance(NMR) spectroscopy. The measurement data are shown below.

¹H NMR (CDCl₃, 300 M Hz): δ=7.44-7.70 (m, 15H), 7.82-7.86 (m, 4H),8.15-8.22 (m, 4H), 8.57 (d, J=1.5, 2H)

In addition, ¹H NMR charts are shown in FIGS. 61A and 61B. Note thatFIG. 61B is a chart where the range of from 7 ppm to 9 ppm in FIG. 61Ais enlarged. The measurement results showed that DBT2PC-II, which is thecarbazole derivative represented by the above structural formula (9),was obtained. Note that the Rf values of DBT2PC-II and3,6-dibromo-9-phenyl-9H-carbazole were respectively 0.41 and 0.51, whichwere found by silica gel thin layer chromatography (TLC) (a developingsolvent in which the ethyl acetate/hexane ratio was 1:10).

Further, an absorption spectrum of DBT2PC-II in a toluene solution ofDBT2PC-II is shown in FIG. 62, and an absorption spectrum of a thin filmof DBT2PC-II is shown in FIG. 63. An ultraviolet-visiblespectrophotometer (V-550, manufactured by JASCO Corporation) was usedfor the measurements of the absorption spectra. In the case of thetoluene solution, the measurements were made with the toluene solutionof DBT2PC-II put in a quartz cell, and the absorption spectrum obtainedby subtraction of the absorption spectra of quartz and toluene from themeasured spectra is shown in the drawing. In addition, as for theabsorption spectrum of the thin film, a sample was prepared byevaporation of DBT2PC-II on a quartz substrate, and the absorptionspectrum obtained by subtraction of that of quartz from the measuredspectra is shown in the drawing. In FIG. 62 and FIG. 63, the horizontalaxis represents wavelength (nm) and the vertical axis representsabsorption intensity (arbitrary unit).

An emission spectrum of DBT2PC-II in the toluene solution of DBT2PC-IIis shown in FIG. 64, and an emission spectrum of a thin film is shown inFIG. 65. As in the measurements of the absorption spectra, anultraviolet-visible spectrophotometer (V-550, manufactured by JASCOCorporation) was used for the measurements. The emission spectrum wasmeasured with the toluene solution of DBT2PC-II put in a quartz cell,and the emission spectrum of the thin film was measured with a sampleprepared by evaporation of DBT2PC-II on a quartz substrate. FIG. 64shows that the maximum emission wavelengths of DBT2PC-II in the toluenesolution of DBT2PC-II were around 368 nm and 385 nm (at an excitationwavelength of 300 nm) and FIG. 65 shows that the greatest emissionwavelength of the thin film of DBT2PC-II was around 400 nm (at anexcitation wavelength of 341 nm).

Further, the ionization potential of DBT2PC-II in a thin film state wasmeasured by a photoelectron spectrometer (AC-2, manufactured by RikenKeiki, Co., Ltd.) in air. The obtained value of the ionization potentialwas converted to a negative value, so that the HOMO level of DBT2PC-IIwas −5.72 eV. From the data of the absorption spectra of the thin filmin FIG. 63, the absorption edge of DBT2PC-II, which was obtained fromTauc plot with an assumption of direct transition, was 3.40 eV.Therefore, the optical energy gap of DBT2PC-II in the solid state wasestimated at 3.40 eV; from the values of the HOMO level obtained aboveand this energy gap, the LUMO level of DBT2PC-II was able to beestimated at −2.32 eV. It was thus found that DBT2PC-II had a wideenergy gap of 3.40 eV in the solid state.

Further, the oxidation reaction characteristics of DBT2PC-II weremeasured. The oxidation reaction characteristics were examined by cyclicvoltammetry (CV) measurements. Note that an electrochemical analyzer(ALS model 600A or 600C, manufactured by BAS Inc.) was used for themeasurements.

For a solution for the CV measurements, dehydrated N,N-dimethylformamide(DMF, product of Sigma-Aldrich Inc., 99.8%, catalog No. 22705-6) wasused as a solvent, and tetra-n-butylammonium perchlorate (n-Bu₄NClO₄,product of Tokyo Chemical Industry Co., Ltd., catalog No. T0836), whichwas a supporting electrolyte, was dissolved in the solvent such that theconcentration thereof was 100 mmol/L. Further, the object to be measuredwas also dissolved in the solvent such that the concentration thereofwas 2 mmol/L. A platinum electrode (a PTE platinum electrode, product ofBAS Inc.) was used as a working electrode; a platinum electrode (a VC-3Pt counter electrode (5 cm), product of BAS Inc.) was used as anauxiliary electrode; and an Ag/Ag⁺ electrode (an RE5 nonaqueous solventreference electrode, product of BAS Inc.) was used as a referenceelectrode. Note that the measurements were conducted at room temperature(20° C. to 25° C.). The scan rates for the CV measurements wereuniformly set to 0.1 V/s.

In the measurements, scanning in which the potential of the workingelectrode with respect to the reference electrode was changed from −0.35V to 1.50 V and then changed from 1.50 V to −0.35 V was one cycle, and100 cycles were performed.

The measurement results revealed that DBT2PC-II showed propertieseffective against repetition of redox reactions between an oxidizedstate and a neutral state without a large variation in oxidation peakeven after the 100 cycles in the measurements.

Further, the HOMO level of DBT2PC-II was determined also by calculationfrom the CV measurement results.

First, the potential energy of the reference electrode with respect tothe vacuum level used was found to be −4.94 eV, as determined in Example6. The oxidation peak potential E_(pa) of DBT2PC-II was 1.20 V. Inaddition, the reduction peak potential E_(pc) thereof was 0.81 V.Therefore, a half-wave potential (an intermediate potential betweenE_(pa) and E_(pc)) can be calculated at 1.01 V. This means thatDBT2PC-II is oxidized by an electric energy of 1.01 [V versus Ag/Ag⁺],and this energy corresponds to the HOMO level. Here, since the potentialenergy of the reference electrode, which was used in this example, withrespect to the vacuum level is −4.94 [eV] as described above, the HOMOlevel of DBT2PC-II was calculated as follows: −4.94−1.01=−5.95 [eV].

Example 13 Synthesis Example 8

In this example is described a method of synthesizing2,7-di-(dibenzothiophen-4-yl)-9-phenyl-9H-carbazole (abbreviation:2,7DBT2PC-II), which is one of the carbazole derivatives described inEmbodiment 1. A structure of 2,7DBT2PC-II is illustrated in thefollowing structural formula (10).

Step 1: Synthesis of 2,7-Di-(dibenzothiophen-4-yl)-9H-carbazole

In a 200-mL three-neck flask were mixed 3.3 g (10 mmol) of2,7-dibromo-9H-carbazole, 6.0 g (21 mmol) of dibenzofuran-4-boronicacid, 11 mg (0.1 mmol) of palladium(II) acetate, 30 mg (0.1 mmol) oftris(ortho-tolyl)phosphine, 50 mL of toluene, 5 mL of ethanol, and 7.5mL of a 2 mol/L aqueous potassium carbonate solution. This mixture wasdegassed while being stirred under reduced pressure, and then heated andstirred at 90° C. for 4.5 hours in a nitrogen atmosphere to be reacted.After the reaction, this reaction mixture solution was cooled to roomtemperature, and then filtered to give a residue. This residue washeated and stirred in a mixed solution of ethanol/water, and wasfiltered to give 4.9 g of a white powder in 92% yield. The synthesisscheme of Step 1 is illustrated in (D-8).

Step 2: Synthesis of 2,7-Di-(dibenzothiophen-4-yl)-9-phenyl-9H-carbazole(abbreviation: 2,7DBT2PC-II)

In a 200-mL three-neck flask were mixed 0.7 g (4.3 mmol) of iodobenzene,1.7 g (3.2 mmol) of 2,7-di-(dibenzothiophen-4-yl)-9H-carbazole, 0.6 g(5.5 mmol) of sodium tert-butoxide, and 36 mg (0.1 mmol) ofbis(dibenzylideneacetone)palladium(0), and the air in the flask wasreplaced with nitrogen. Then, 5 mL of dehydrated xylene was added tothis mixture. After the mixture was degassed while being stirred underreduced pressure, 0.7 mL (0.3 mmol) of tri(tert-butyl)phosphine (10 wt %hexane solution) was added to the mixture. This mixture was stirred at120° C. for 5 hours in a nitrogen atmosphere to be reacted. After thereaction, 300 mL of toluene was added to this reaction mixture solution,and this suspension was filtered through Florisil and Celite. Theresulting filtrate was concentrated, followed by purification by silicagel column chromatography (toluene as the developing solvent). Thefraction thus obtained was concentrated, acetone and methanol were addedthereto, and the mixture was irradiated with ultrasonic waves. Then,recrystallization gave 1.9 g of a white powder in 93% yield. The abovesynthesis method is illustrated in (E-8) below.

The obtained white powder was subjected to nuclear magnetic resonance(NMR) spectroscopy. The measurement data are shown below.

¹H NMR (CDCl₃, 300 M Hz): δ (ppm)=7.39-7.50 (m, 5H), 7.53-7.62 (m, 6H),7.70-7.74 (m, 4H), 7.81-7.87 (m, 4H), 8.12-8.21 (m, 4H), 8.32 (d, J=8.1,2H)

In addition, ¹H NMR charts are shown in FIGS. 66A and 66B. Themeasurement results showed that 2,7DBT2PC-II, which is the carbazolederivative represented by the above structural formula (910 wasobtained. Note that the Rf values of 2,7DBT2PC-II and2,7-di-(dibenzothiophen-4-yl)-9H-carbazole were respectively 0.41 and0.22, which were found by silica gel thin layer chromatography (TLC) (adeveloping solvent in which the ethyl acetate/hexane ratio was 1:5).

Further, an absorption spectrum of 2,7DBT2PC-II in a toluene solution of2,7DBT2PC-II is shown in FIG. 67, and an absorption spectrum of a thinfilm of 2,7DBT2PC-II is shown in FIG. 68. An ultraviolet-visiblespectrophotometer (V-550, manufactured by JASCO Corporation) was usedfor the measurements of the absorption spectra. In the case of thetoluene solution, the measurements were made with the toluene solutionof 2,7DBT2PC-II put in a quartz cell, and the absorption spectrumobtained by subtraction of the absorption spectra of quartz and toluenefrom the measured spectra is shown in the drawing. In addition, as forthe absorption spectrum of the thin film, a sample was prepared byevaporation of 2,7DBT2PC-II on a quartz substrate, and the absorptionspectrum obtained by subtraction of that of quartz from the measuredspectra is shown in the drawing. In FIG. 67 and FIG. 68, the horizontalaxis represents wavelength (nm) and the vertical axis representsabsorption intensity (arbitrary unit).

An emission spectrum of 2,7DBT2PC-II in the toluene solution of2,7DBT2PC-II is shown in FIG. 69, and an emission spectrum of the thinfilm of 2,7DBT2PC-II is shown in FIG. 70. As in the measurements of theabsorption spectra, an ultraviolet-visible spectrophotometer (V-550,manufactured by JASCO Corporation) was used for the measurements. Theemission spectrum was measured with the toluene solution of 2,7DBT2PC-IIput in a quartz cell, and the emission spectrum of the thin film wasmeasured with a sample prepared by evaporation of 2,7DBT2PC-II on aquartz substrate. FIG. 69 shows that the maximum emission wavelengths of2,7DBT2PC-II in the toluene solution of 2,7DBT2PC-II were around 381 nmand 395 nm (at an excitation wavelength of 345 nm) and FIG. 70 showsthat the greatest emission wavelength of the thin film of 2,7DBT2PC-IIwas around 411 nm (at an excitation wavelength of 347 nm).

Further, the ionization potential of 2,7DBT2PC-II in a thin film statewas measured by a photoelectron spectrometer (AC-2, manufactured byRiken Keiki, Co., Ltd.) in air. The obtained value of the ionizationpotential was converted to a negative value, so that the HOMO level of2,7DBT2PC-II was −5.79 eV. From the data of the absorption spectra ofthe thin film in FIG. 68, the absorption edge of 2,7DBT2PC-II, which wasobtained from Tauc plot with an assumption of direct transition, was3.25 eV. Therefore, the optical energy gap of 2,7DBT2PC-II in the solidstate was estimated at 3.25 eV; from the values of the HOMO levelobtained above and this energy gap, the LUMO level of 2,7DBT2PC-II wasable to be estimated at −2.54 eV. It was thus found that 2,7DBT2PC-IIhad a wide energy gap of 3.25 eV in the solid state.

Further, the oxidation reaction characteristics of 2,7DBT2PC-II weremeasured. The oxidation reaction characteristics were examined by cyclicvoltammetry (CV) measurements. Note that an electrochemical analyzer(ALS model 600A or 600C, manufactured by BAS Inc.) was used for themeasurements.

For a solution for the CV measurements, dehydrated N,N-dimethylformamide(DMF, product of Sigma-Aldrich Inc., 99.8%, catalog No. 22705-6) wasused as a solvent, and tetra-n-butylammonium perchlorate (n-Bu₄NClO₄,product of Tokyo Chemical Industry Co., Ltd., catalog No. T0836), whichwas a supporting electrolyte, was dissolved in the solvent such that theconcentration thereof was 100 mmol/L. Further, the object to be measuredwas also dissolved in the solvent such that the concentration thereofwas 2 mmol/L. A platinum electrode (a PTE platinum electrode, product ofBAS Inc.) was used as a working electrode; a platinum electrode (a VC-3Pt counter electrode (5 cm), product of BAS Inc.) was used as anauxiliary electrode; and an Ag/Ag⁺ electrode (an RE5 nonaqueous solventreference electrode, product of BAS Inc.) was used as a referenceelectrode. Note that the measurements were conducted at room temperature(20° C. to 25° C.). The scan rates for the CV measurements wereuniformly set to 0.1 V/s.

In the measurements, scanning in which the potential of the workingelectrode with respect to the reference electrode was changed from −0.13V to 1.50 V and then changed from 1.50 V to −0.13 V was one cycle, and100 cycles were performed.

The measurement results revealed that 2,7DBT2PC-II showed propertieseffective against repetition of redox reactions between an oxidizedstate and a neutral state without a large variation in oxidation peakeven after the 100 cycles in the measurements.

Further, the HOMO level of 2,7DBT2PC-II was determined also bycalculation from the CV measurement results.

First, the potential energy of the reference electrode with respect tothe vacuum level used was found to be −4.94 eV, as determined in Example6. The oxidation peak potential E_(pa) of 2,7DBT2PC-II was 1.23 V. Inaddition, the reduction peak potential E_(pc) thereof was 0.93 V.Therefore, a half-wave potential (an intermediate potential betweenE_(pa) and E_(pc)) can be calculated at 1.08 V. This means that2,7DBT2PC-II is oxidized by an electric energy of 1.01 [V versusAg/Ag⁺], and this energy corresponds to the HOMO level. Here, since thepotential energy of the reference electrode, which was used in thisexample, with respect to the vacuum level is −4.94 [eV] as describedabove, the HOMO level of 2,7DBT2PC-II was calculated as follows:−4.94−1.08=−6.02 [eV].

Example 14 Synthesis Example 9

In this example is described a method of synthesizing3,6-di-(dibenzofuran-4-yl)-9-phenyl-9H-carbazole (abbreviation:DBF2PC-II), which is one of the carbazole derivatives described inEmbodiment 1. A structure of DBF2PC-II is illustrated in the followingstructural formula (11).

Synthesis of 3,6-Di(dibenzofuran-4-yl)-9-phenyl-9H-carbazole(abbreviation: DBF2PC-II)

To a 200-mL three-neck flask were added 2.0 g (5.0 mmol) of3,6-dibromo-9-phenyl-9H-carbazole, 3.2 g (11 mmol) ofdibenzofuran-4-boronic acid, 10 mg (0.1 mmol) of palladium(II) acetate,30 mg (0.1 mmol) of tris(o-tolyl)phosphine, 50 mL of toluene, 5 mL ofethanol, and 7.5 mL of a 2 mol/L aqueous potassium carbonate solution.This mixture was degassed while being stirred under reduced pressure,and then heated and stirred at 90° C. for 6.5 hours under a nitrogenstream to be reacted.

After the reaction, 250 mL of toluene was added to this reaction mixtureand the mixture was heated. The mixture was suction-filtered throughCelite (produced by Wako Pure Chemical Industries, Ltd., Catalog No.531-16855), alumina, and Florisil (produced by Wako Pure ChemicalIndustries, Ltd., Catalog No. 540-00135) in this order to give afiltrate. The resulting filtrate was purified by silica gel columnchromatography (a developing solvent in which the toluene/hexane ratiowas 1:3). The obtained fraction was concentrated, acetone, methanol, andwater were added thereto, and the mixture was irradiated with ultrasonicwaves. Then, acetone and methanol were added to the obtained precipitateand the mixture was washed while being irradiated with ultrasonic waves,so that 2.8 g of a white powder which was the object of the synthesiswas obtained in 69% yield. The synthesis scheme of the above synthesismethod is illustrated in (c-9) below.

The Rf values of the white powder obtained through the above reactionand 3,6-dibromo-9-phenyl-9H-carbazole were respectively 0.32 and 0.55,which were found by silica gel thin layer chromatography (TLC) (adeveloping solvent in which the ethyl acetate/hexane ratio was 1:10).

The white powder obtained by the above Step 1 was subjected to nuclearmagnetic resonance (NMR) spectroscopy. The measurement data are shownbelow. In addition, ¹H NMR charts are shown in FIGS. 71A and 71B. Notethat FIG. 71B is an enlarged chart of FIG. 71A. The measurement resultsconfirmed that the white powder obtained by the above Step 1 wasDBF2PC-II, which is represented by the above structural formula (11).

¹H NMR (CDCl₃, 300 M Hz): δ (ppm)=7.37 (dt, J=7.8 Hz, J=1.2 Hz, 2H),7.44-7.56 (m, 5H), 7.60-7.69 (m, 8H), 7.75 (dd, J=7.2 Hz, J=1.5 Hz, 2H),7.95 (dd, J=7.8 Hz, J=1.5 Hz, 2H), 8.00-8.04 (m, 4H), 8.75 (d, J=1.5 Hz,2H).

Further, an absorption and emission spectra of DBF2PC-II in a toluenesolution of DBF2PC-II are shown in FIG. 72A, and an absorption andemission spectra of a thin film of DBF2PC-II are shown in FIG. 72B. Anultraviolet-visible spectrophotometer (V-550, manufactured by JASCOCorporation) was used for the measurements of the spectra. The spectraof the toluene solution were measured with a toluene solution ofDBF2PC-II put in a quartz cell. The spectra of the thin film weremeasured with a sample prepared by evaporation of DBF2PC-II on a quartzsubstrate. Note that as the absorption spectrum of the toluene solution,the absorption spectrum obtained by subtraction of the absorptionspectra of quartz and toluene from the measured spectra is shown in thedrawing, and as the absorption spectrum of the thin film, the absorptionspectrum obtained by subtraction of that of quartz from the measuredspectra is shown in the drawing.

FIGS. 72A and 72B show that the maximum absorption wavelength ofDBF2PC-II in the toluene solution of DBF2PC-II was around 320 nm, themaximum emission wavelengths thereof were around 370 nm and 387 nm (atan excitation wavelength of 290 nm), the maximum absorption wavelengthsof the thin film of DBF2PC-II were around 325 nm, 294 nm, 253 nm, and205 nm, and the maximum emission wavelengths thereof were around 401 nmand 382 nm (at an excitation wavelength of 325 nm).

The absorption spectra reveal that DBF2PC-II described in this exampleis a material that shows almost no absorption in the visible region.Further, the emission spectra reveal that the light emission is bluishviolet.

Further, the ionization potential of DBF2PC-II in a thin film state wasmeasured by a photoelectron spectrometer (AC-2, manufactured by RikenKeiki, Co., Ltd.) in air. The obtained value of the ionization potentialwas converted to a negative value, so that the HOMO level of DBF2PC-IIwas −5.67 eV. From the data of the absorption spectra of the thin filmin FIG. 72, the absorption edge of DBF2PC-II, which was obtained fromTauc plot with an assumption of direct transition, was 3.40 eV.Therefore, the optical band gap of DBF2PC-II in the solid state wasestimated at 3.40 eV; from the values of the HOMO level obtained aboveand this band gap, the LUMO level of DBF2PC-II was able to be estimatedat −2.27 eV. It was thus found that DBF2PC-II had a wide band gap of3.40 eV in the solid state and also had a relatively deep HOMO level.

Further, thermophysical properties of DBF2PC-II were measured with adifferential scanning calorimeter (DSC, manufactured by PerkinElmer,Inc., Pyris 1). First, a sample was heated from −10° C. up to 350° C. ata temperature rising rate of 40° C./min, and then it was cooled to −10°C. at 40° C./min. After that, heating was performed up to 290° C. at atemperature rising rate of 10° C./min, and thus a DSC chart wasobtained. As can be seen from the DSC chart, a peak indicating the glasstransition temperature of DBF2PC-II was observed, which showed the glasstransition temperature (Tg) was 131° C. Thus, DBF2PC-II has a high glasstransition point. Therefore, it was confirmed that DBF2PC-II of thissynthesis example had high heat resistance.

Example 15

In this example described is a light-emitting element in which3,6-di(dibenzofuran-4-yl)-9-phenyl-9H-carbazole (abbreviation:DBF2PC-II, a structural formula (11)), which is one of the carbazolederivatives represented by the general formula (G1), is used as amaterial for a hole-transport layer adjacent to a light-emitting layerusing an emission center substance that emits blue fluorescence.

The molecular structures of organic compounds used in this example arerepresented by the structural formulae (11), (iv), (viii), and (ix)below.

In the element structure in FIG. 1A, an electron-injection layer isprovided between an electron-transport layer 114 and a second electrode104.

Fabrication of Light-Emitting Element 9

First, a glass substrate 101 over which indium tin oxide containingsilicon (ITSO) with a thickness of 110 nm was formed as a firstelectrode 102 was prepared. The periphery of a surface of the ITSO wascovered with a polyimide film so that an area of 2 mm×2 mm of thesurface was exposed. The electrode area was 2 mm×2 mm. As a pretreatmentfor forming the light-emitting element over the substrate, the surfaceof the substrate was washed with water and baked at 200° C. for onehour, and then a UV ozone treatment was performed for 370 seconds. Then,the substrate was transferred into a vacuum evaporation apparatus whosepressure was reduced to about 10⁻⁴ Pa, vacuum baking at 170° C. for 30minutes was performed in a heating chamber of the vacuum evaporationapparatus, and then the substrate was cooled down for about 30 minutes.

Then, the substrate was fixed on a holder provided in the vacuumevaporation apparatus such that the surface of the substrate 101provided with ITSO faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, a hole-injection layer 111 was formed by co-evaporation of3,6-di(dibenzofuran-4-yl)-9-phenyl-9H-carbazole (abbreviation:DBF2PC-II) represented by the above structural formula (11) andmolybdenum(VI) oxide such that the ratio of DBF2PC-II:molybdenum(VI)oxide was 2:1 (weight ratio). The thickness of was the layer was set to50 nm. Note that the co-evaporation is an evaporation method in which aplurality of different substances is concurrently vaporized from therespective different evaporation sources.

Next, DBF2PC-II was evaporated to a thickness of 10 nm, so that thehole-transport layer 112 was formed.

Further, the light-emitting layer 113 was formed on the hole-transportlayer 112 in such a way that9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA)represented by the above structural formula (viii) andN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn) represented by the above structuralformula (ix) were evaporated to form a 30-nm-thick film so that theratio of CzPA to 1,6mMemFLPAPrn was 1:0.05 (weight ratio).

Next, on the light-emitting layer 113, CzPA was evaporated to athickness of 10 nm, and then bathophenanthroline (abbreviation: BPhen)represented by the above structural formula (iv) was evaporated to athickness of 15 nm, so that the electron-transport layer 114 was formed.Then, lithium fluoride was evaporated to a thickness of 1 nm on theelectron-transport layer 114, so that the electron-injection layer wasformed. Lastly, an aluminum film was formed to a thickness of 200 nm asthe second electrode 104 functioning as a cathode, so that thelight-emitting element 9 was completed. Note that in the aboveevaporation processes, evaporation was all performed by a resistanceheating method.

[Operation Characteristics of Light-Emitting Element 9]

The light-emitting element 9 thus obtained was sealed in a glove boxunder a nitrogen atmosphere without being exposed to the air. Then, theoperation characteristics of the light-emitting element were measured.Note that the measurements were carried out at room temperature (in anatmosphere kept at 25° C.).

FIG. 73 shows luminance versus voltage characteristics of thelight-emitting element 9, FIG. 74 shows current efficiency versusluminance characteristics thereof, FIG. 75 shows current versus voltagecharacteristics thereof, FIG. 76 shows power efficiency versus luminancecharacteristics thereof, and FIG. 77 shows external quantumefficiency-luminance characteristics thereof.

FIG. 74 reveals that the light-emitting element, in which the carbazolederivative represented by the general formula (G1) is used as a materialfor a hole-transport layer in contact with a light-emitting layer foremitting blue fluorescence, has favorable current efficiency versusluminance characteristics and high emission efficiency. This is becausethe carbazole derivative represented by the general formula (G1) has ahigh T1 level, and thus transfer of excitation energy can be suppresseddespite the adjacency to a light-emitting substance that emits bluefluorescence and has a wide energy gap. In addition, FIG. 73 revealsthat the light-emitting, in which the carbazole derivative representedby the general formula (G1) is used as a material for a hole-transportlayer adjacent to a light-emitting layer for emitting bluephosphorescence, has favorable luminance versus voltage characteristicsand can be driven with a low voltage. This indicates that any of thecarbazole derivatives represented by the general formula (G1) has anexcellent carrier-transport property. Further, FIG. 76 and FIG. 77reveal that light-emitting element 9 has excellent power efficiencyversus luminance characteristics and excellent external quantumefficiency-luminance characteristics.

FIG. 78 shows an emission spectrum when a current of 1 mA was made toflow in the fabricated light-emitting element 9. The emission intensityis shown as a value relative to the greatest emission intensity assumedto be 1. FIG. 78 reveals that the light-emitting element 9 emits bluelight due to 1,6mMemFLPAPrn, which is the emission center substance.

Next, the initial luminance is set at 5000 cd/m², the element was drivenunder a condition where the current density was constant, and changes inluminance with respect to the driving time were examined. FIG. 79 showsnormalized luminance versus time characteristics. From FIG. 79, it isfound that the light-emitting element 9 shows favorable characteristicsand has high reliability.

Example 16 Synthesis Example 10

In this example is described a method of synthesizing3,3′-di(dibenzothiophen-4-yl)-N,N′-(1,3-phenylene)bicarbazole(abbreviation: mDBTCz2P-II), which is one of the carbazole derivativesdescribed in Embodiment 1. A structure of mDBTCz2P-II is illustrated inthe following structural formula (12).

Step 1: Synthesis of 3-(Dibenzothiophen-4-yl)-9H-carbazole

This was synthesized as in Step 1 in Synthesis Example 1.

Step 2: Synthesis of3,3′-Di(dibenzothiophen-4-yl)-N,N′-(1,3-phenylene)bicarbazole(abbreviation: mDBTCz2P-II)

In a 200-mL three-neck flask were put 1.2 g (5.0 mmol) of1,3-dibromobenzene and 3.5 g (10 mmol) of3-(dibenzothiophen-4-yl)-9H-carbazole (abbreviation: DBTCz), and the airin the flask was replaced with nitrogen. To this mixture were added 40mL of toluene, 0.10 mL of tri(tert-butyl)phosphine (a 10 wt % hexanesolution), and 0.98 g (10 mmol)) of sodium tert-butoxide. This mixturewas degassed while being stirred under reduced pressure. After thismixture was stirred at 80° C. and dissolution of the materials wasconfirmed, 61 mg (0.11 mmol) of bis(dibenzylideneacetone)palladium(0)was added thereto. This mixture was refluxed at 110° C. for 55 hours.After the reflux, the mixture was cooled to room temperature, and theprecipitated white solid was collected by suction filtration. Theobtained solid was washed with water and toluene to give 1.2 g of awhite solid which was the object of the synthesis in 70% yield. Thesynthesis scheme of Step 2 is illustrated in the following formula(f-10).

By a train sublimation method, 1.1 g of the obtained white solid waspurified. The purification was conducted by heating of the white solidat 350° C. under a pressure of 2.8 Pa with a flow rate of argon gas of10 mL/min. After the purification, 0.89 g of a colorless transparentsolid was obtained in a yield of 83%.

This compound was subjected to nuclear magnetic resonance (NMR)spectroscopy. In addition, ¹H NMR charts are shown in FIGS. 80A and 80B.Note that FIG. 80B is a chart where the range of from 7 ppm to 9 ppm inFIG. 80A is enlarged. In addition, ¹H NMR data of the obtained compoundare shown below.

¹H NMR (CDCl₃, 300 M Hz): δ(ppm)=7.36 (td, J₁=0.9 Hz, J₂=7.8 Hz, 2H),7.43-7.53 (m, 6H), 7.58-7.63 (m, 6H), 7.71 (d, J=8.7 Hz, 2H), 7.80-7.97(m, 8H), 8.15-8.24 (m, 6H), 8.53 (d, J=1.5 Hz, 2H)

It is thus confirmed that the solid obtained in this synthesis examplewas 3,3′-di(dibenzothiophen-4-yl)-N,N′-(1,3-phenylene)bicarbazole(abbreviation: mDBTCz2P-II).

Further, an absorption and emission spectra of mDBTCz2P-II in a toluenesolution of mDBTCz2P-II are shown in FIG. 81A, and an absorption andemission spectra of a thin film of mDBTCz2P-II are shown in FIG. 81B. Anultraviolet-visible spectrophotometer (V-550, manufactured by JASCOCorporation) was used for the measurements of the spectra. The spectraof the toluene solution were measured with a toluene solution ofmDBTCz2P-II put in a quartz cell. The spectra of the thin film weremeasured with a sample prepared by evaporation of mDBTCz2P-II on aquartz substrate. Note that as the absorption spectrum of the toluenesolution, the absorption spectrum obtained by subtraction of theabsorption spectra of only the quartz cell and toluene from the measuredspectra is shown in the drawing, and as the absorption spectrum of thethin film, the absorption spectrum obtained by subtraction of that ofthe quartz substrate from the measured spectra is shown in the drawing.

FIG. 81A shows that the absorption peak wavelengths of mDBTCz2P-II inthe toluene solution of mDBTCz2P-II were around 332 nm, 288 nm and 281nm, and the emission peak wavelength thereof was around 370 nm (at anexcitation wavelength of 334 nm). Further, FIG. 81B shows that theabsorption peak wavelengths of the thin film of mDBTCz2P-II were around337 nm, 294 nm, 246 nm and 209 nm, and the emission peak wavelengthsthereof were around 393 nm and 380 nm (at an excitation wavelength of342 nm).

Further, the ionization potential of mDBTCz2P-II in a thin film statewas measured by a photoelectron spectrometer (AC-2, manufactured byRiken Keiki, Co., Ltd.) in air. The obtained value of the ionizationpotential was converted to a negative value, so that the HOMO level ofmDBTCz2P-II was −5.93 eV. From the data of the absorption spectra of thethin film in FIG. 81B, the absorption edge of mDBTCz2P-II, which wasobtained from Tauc plot with an assumption of direct transition, was3.45 eV. Therefore, the optical energy gap of mDBTCz2P-II in the solidstate was estimated at 3.45 eV; from the values of the HOMO levelobtained above and this energy gap, the LUMO level of mDBTCz2P-II wasable to be estimated at −2.48 eV. It was thus found that mDBTCz2P-II hada wide energy gap of 3.45 eV in the solid state.

Example 17

In this example described is a light-emitting element in which3,3′-di(dibenzothiophen-4-yl)-N,N′-(1,3-phenylene)bicarbazole(abbreviation: mDBTCz2P-II, a structural formula (12)), which is acarbazole derivative described in Embodiment 1, is used as a materialfor a hole-transport layer adjacent to a light-emitting layer using anemission center substance that emits blue fluorescence. Note that inthis example, mDBTCz2P-II is also used for a composite material withmolybdenum oxide in a hole-injection layer.

The molecular structures of organic compounds used in this example arerepresented by the structural formulae (iv), (viii), (ix), and (12)below. In the element structure in FIG. 1A, an electron-injection layeris provided between an electron-transport layer 114 and a secondelectrode 104.

[Fabrication of Light-Emitting Element 10]

First, a glass substrate 101 over which indium tin oxide containingsilicon (ITSO) with a thickness of 110 nm was formed as a firstelectrode 102 was prepared. The periphery of a surface of the ITSO wascovered with a polyimide film so that an area of 2 mm×2 mm of thesurface was exposed. The electrode area was 2 mm×2 mm. As a pretreatmentfor forming the light-emitting element over the substrate, the surfaceof the substrate was washed with water and baked at 200° C. for onehour, and then a UV ozone treatment was performed for 370 seconds. Then,the substrate was transferred into a vacuum evaporation apparatus whosepressure was reduced to about 10⁻⁴ Pa, vacuum baking at 170° C. for 30minutes was performed in a heating chamber of the vacuum evaporationapparatus, and then the substrate was cooled down for about 30 minutes.

Then, the substrate was fixed on a holder provided in the vacuumevaporation apparatus such that the surface of the substrate 101provided with ITSO faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, a hole-injection layer 111 was formed by co-evaporation of3,3′-di(dibenzothiophen-4-yl)-N,N′-(1,3-phenylene)bicarbazole(abbreviation: mDBTCz2P-II), which is a carbazole derivative describedin Embodiment 1 represented by the above structural formula (12), andmolybdenum(VI) oxide such that the ratio of mDBTCz2P-II:molybdenum(VI)oxide was 2:1 (weight ratio). The thickness of was the layer was set to50 nm. Note that the co-evaporation is an evaporation method in which aplurality of different substances is concurrently vaporized from therespective different evaporation sources.

Next, mDBTCz2P-II was evaporated to a thickness of 10 nm, so that thehole-transport layer 112 was formed.

Further, the light-emitting layer 113 was formed on the hole-transportlayer 112 in such a way that9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA),which is the carbazole derivative represented by the above structuralformula (viii), andN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn) represented by the above structuralformula (ix) were evaporated to form a 30-nm-thick film so that theratio of CzPA to 1,6mMemFLPAPrn was 1:0.04 (weight ratio).

Next, CzPA was evaporated to a thickness of 10 nm, and thenbathophenanthroline (abbreviation: BPhen) represented by the abovestructural formula (iv) was evaporated to a thickness of 15 nm, so thatthe electron-transport layer 114 was formed.

Further, lithium fluoride was evaporated to a thickness of 1 nm on theelectron-transport layer 114, so that the electron-injection layer wasformed. Lastly, an aluminum film was formed to a thickness of 200 nm asthe second electrode 104 functioning as a cathode, so that thelight-emitting element 10 was completed. Note that in the aboveevaporation processes, evaporation was all performed by a resistanceheating method.

[Operation Characteristics of Light-Emitting Element 10]

The light-emitting element 10 thus obtained was sealed in a glove boxunder a nitrogen atmosphere without being exposed to the air. Then, theoperation characteristics of the light-emitting element were measured.Note that the measurements were carried out at room temperature (in anatmosphere kept at 25° C.).

FIG. 82 shows luminance versus current density characteristics of thelight-emitting element 10, FIG. 83 shows luminance versus voltagecharacteristics thereof, FIG. 84 shows current efficiency versusluminance characteristics thereof, and FIG. 85 shows current versusvoltage characteristics thereof. In FIG. 82, the vertical axisrepresents luminance (cd/m²), and the horizontal axis represents currentdensity (mA/cm²). In FIG. 83, the vertical axis represents luminance(cd/m²), and the horizontal axis represents voltage (V). In FIG. 84, thevertical axis represents current efficiency (cd/A), and the horizontalaxis represents luminance (cd/m²). In FIG. 85, the vertical axisrepresents current (mA), and the horizontal axis represents voltage (V).

FIG. 82 reveals that the light-emitting element, in which the carbazolederivative represented by the general formula (G1) is used as ahole-transport material adjacent to a light-emitting layer for emittingblue fluorescence and used for a hole-injection layer (as a compositematerial with molybdenum oxide), has favorable luminance versus currentefficiency characteristics and high emission efficiency. Here, CzPA asthe host material of the light-emitting layer in the light-emittingelement 10 is a material having a relatively high electron-transportproperty. It is therefore understood that the light-emitting region inthe light-emitting layer is localized on the hole-transport layer side.A reason why the light-emitting element having high emission efficiencycan be obtained even in such a state is that any of the carbazolederivatives represented by the general formula (G1) has a wide energygap. Since mDBTCz2P-II, which is any of the carbazole derivativesdescribed in Embodiment 1, has a wide energy gap, even when it is usedfor the hole-transport layer adjacent to the emission center substancethat emits blue fluorescence, a reduction in emission efficiency issuppressed without transfer of excitation energy to the hole-transportlayer.

In addition, FIG. 83 reveals that the light-emitting element, in whichthe carbazole derivative represented by the general formula (G1) is usedas a host material for a light-emitting layer for emitting bluefluorescence, has favorable luminance versus voltage characteristics andcan be driven with a low voltage. This indicates that any of thecarbazole derivatives represented by the general formula (G1) has anexcellent carrier-transport property and the composite materialincluding any of the carbazole derivatives represented by the generalformula (G1) has an excellent carrier-injection property.

FIG. 86 shows an emission spectrum when a current of 1 mA was made toflow in the fabricated light-emitting element 10. In FIG. 86, thevertical axis represents emission intensity (arbitrary unit), and thehorizontal axis represents wavelength (nm). The emission intensity isshown as a value relative to the greatest emission intensity assumed tobe 1. FIG. 86 reveals that the light-emitting element 10 emits bluelight due to 1,6mMemFLPAPrn, which is the emission center substance.

Next, the initial luminance is set at 1000 cd/m², the light-emittingelement 10 was driven under a condition where the current density wasconstant, and changes in luminance with respect to the driving time wereexamined. FIG. 87 shows normalized luminance versus timecharacteristics. From FIG. 87, it is found that the light-emittingelement 10 shows favorable characteristics and has high reliability.

Example 18

In this example described is a light-emitting element (light-emittingelement 11) in which an emission center substance that emits bluephosphorescence is used for a light-emitting layer and3,3′-di(dibenzothiophen-4-yl)-N,N′-(1,3-phenylene)bicarbazole(abbreviation: mDBTCz2P-II, a structural formula (12)) which is ancarbazole derivative described Embodiment 1, is used as a host materialfor the light-emitting layer, and of a light-emitting element(light-emitting element 12) in which an emission center substance thatemits blue phosphorescence is used for a light-emitting layer andmDBTCz2P-II is used as a material for a hole-transport layer adjacent tothe light-emitting layer.

The molecular structures of organic compounds used in this example arerepresented by the structural formulae (iv), (x) to (xiii), and (12)below. In the element structure in FIG. 1A, an electron-injection layeris provided between an electron-transport layer 114 and a secondelectrode 104.

[Fabrication of Light-Emitting Element 11 and Light-Emitting Element 12]

First, a glass substrate 101 over which indium tin oxide containingsilicon (ITSO) with a thickness of 110 nm was formed as a firstelectrode 102 was prepared. The periphery of a surface of the ITSO wascovered with a polyimide film so that an area of 2 mm×2 mm of thesurface was exposed. The electrode area was 2 mm×2 mm. As a pretreatmentfor forming the light-emitting element over the substrate, the surfaceof the substrate was washed with water and baked at 200° C. for onehour, and then a UV ozone treatment was performed for 370 seconds. Then,the substrate was transferred into a vacuum evaporation apparatus whosepressure was reduced to about 10⁻⁴ Pa, vacuum baking at 170° C. for 30minutes was performed in a heating chamber of the vacuum evaporationapparatus, and then the substrate was cooled down for about 30 minutes.

Then, the substrate was fixed on a holder provided in the vacuumevaporation apparatus such that the surface of the substrate 101provided with ITSO faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, a hole-injection layer 111 was formed by co-evaporation of4,4′-bis(N-carbazolyl)biphenyl (abbreviation: CBP) represented by theabove structural formula (x) and molybdenum(VI) oxide such that theratio of CBP:molybdenum(VI) oxide was 2:1 (weight ratio). The thicknessof was the layer was set to 60 nm. Note that the co-evaporation is anevaporation method in which a plurality of different substances isconcurrently vaporized from the respective different evaporationsources.

Next, 1,3-bis(N-carbazolyl)benzene (abbreviation: mCP) represented bythe above structural formula (xi) was evaporated to a thickness of 20 nmto form the hole-transport layer 112 of the light-emitting element 11,and 3,3′-di(dibenzothiophen-4-yl)-N,N′-(1,3-phenylene)bicarbazole(abbreviation: mDBTCz2P-II) represented by the above structural formula(12) described in Embodiment 1 was evaporated to a thickness of 20 nm toform the hole-transport layer 112 of the light-emitting element 12.

Further, for the light-emitting element 11, the light-emitting layer 113was formed on the hole-transport layer 112 by forming a stacked layer insuch a way that mDBTCz2P-II andtris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III)(abbreviation: [Ir(Mptz1-mp)₃]) represented by the above structuralformula (xii) were evaporated to a thickness of 30 nm so that the ratioof mDBTCz2P-II to [Ir(Mptz1-mp)₃] was 1.0.08 (weight ratio), andthereon, 2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole(abbreviation: mDBTBIm-II) represented by the above structural formula(xiii) and [Ir(Mptz1-mp)₃] were evaporated to a thickness of 10 nm sothat the ratio of mDBTBIm-II to [Ir(Mptz1-mp)₃] was 1:0.08 (weightratio).

For the light-emitting element 12, the light-emitting layer 113 wasfunned by forming a stacked layer in such a way that mCP and[Ir(Mptz1-mp)₃] were evaporated to a thickness of 30 so that the ratioof mCP to [Ir(Mptz1-mp)₃] was 1.0.08 (weight ratio), and thereon,mDBTBIm-II and [Ir(Mptz1-mp)₃] were then evaporated to a thickness of 10so that the ratio of mDBTBIm-II to [Ir(Mptz1-mp)₃] was 1:0.08 (weightratio).

Next, bathophenanthroline (abbreviation: BPhen) represented by the abovestructural formula (iv) was evaporated to a thickness of 15 nm, so thatan electron-transport layer 114 was formed.

Further, lithium fluoride was evaporated to a thickness of 1 nm on theelectron-transport layer 114, so that the electron-injection layer wasformed. Lastly, an aluminum film was formed to a thickness of 200 nm asthe second electrode 104 functioning as a cathode, so that thelight-emitting elements 11 and 12 were completed. Note that in the aboveevaporation processes, evaporation was all performed by a resistanceheating method.

[Operation Characteristics of Light-Emitting Elements 11 and 12]

The light-emitting elements 11 and 12 thus obtained were sealed in aglove box under a nitrogen atmosphere without being exposed to the air.Then, the operation characteristics of these light-emitting elementswere measured. Note that the measurements were carried out at roomtemperature (in an atmosphere kept at 25° C.).

FIG. 88 shows luminance versus current density characteristics of thelight-emitting element 11, FIG. 89 shows luminance versus voltagecharacteristics thereof, FIG. 90 shows current efficiency versusluminance characteristics thereof, and FIG. 91 shows current versusvoltage characteristics thereof. FIG. 92 shows luminance versus currentdensity characteristics of the light-emitting element 12, FIG. 93 showsluminance versus voltage characteristics thereof, FIG. 94 shows currentefficiency versus luminance characteristics thereof, and FIG. 95 showscurrent versus voltage characteristics thereof. In FIG. 88 and FIG. 92,the vertical axis represents luminance (cd/m²), and the horizontal axisrepresents current density (mA/cm²). In FIG. 89 and FIG. 93, thevertical axis represents luminance (cd/m²), and the horizontal axisrepresents voltage (V). In FIG. 90 and FIG. 94, the vertical axisrepresents current efficiency (cd/A), and the horizontal axis representsluminance (cd/m²). In FIG. 91 and FIG. 95, the vertical axis representscurrent (mA), and the horizontal axis represents voltage (V).

FIG. 90 reveals that the light-emitting element 11, in which thecarbazole derivative represented by the general formula (G1) is used asa host material of a light-emitting layer for emitting bluephosphorescence, has favorable luminance versus current characteristicsand high emission efficiency. This is because the carbazole derivativerepresented by the general formula (G1) has a wide energy gap, and thuseven a light-emitting substance that emits blue phosphorescence gap canbe efficiently excited. In addition, FIG. 89 reveals that thelight-emitting element, in which the carbazole derivative represented bythe general formula (G1) is used as a host material of a light-emittingfor emitting blue phosphorescence, has favorable luminance versusvoltage characteristics and can be driven with a low voltage. Thisindicates that any of the carbazole derivatives represented by thegeneral formula (G1) has an excellent carrier-transport property.

FIG. 94 reveals that the light-emitting element 12, in which thecarbazole derivative represented by the general formula (G1) is used asa hole-transport material adjacent to a light-emitting layer foremitting blue phosphorescence, has favorable luminance versus currentefficiency characteristics and high emission efficiency. This is becausesince mDBTCz2P-II, which is any of the carbazole derivatives describedin Embodiment 1, has a wide energy gap and a high triplet excitationenergy accordingly, even when it is used for the hole-transport layeradjacent to the emission center substance that emits bluephosphorescence, a reduction in emission efficiency is suppressedwithout transfer of excitation energy to the hole-transport layer. Inaddition, FIG. 93 reveals that the light-emitting elements in each ofwhich the carbazole derivative represented by the general formula (G1)is used as a host material of a light-emitting layer for emitting bluephosphorescence, has favorable luminance versus voltage characteristicsand can be driven with a low voltage. This indicates that each carbazolederivative represented by the general formula (G1) has an excellentcarrier-transport property.

FIG. 96 shows an emission spectrum when a current of 0.1 mA was made toflow in the fabricated light-emitting element 11, and FIG. 97 shows anemission spectrum when a current of 0.1 mA was made to flow in thelight-emitting element 12. In FIG. 96 and FIG. 97, the vertical axisrepresents absorption intensity (arbitrary unit), and the horizontalaxis represents wavelength (nm). The emission intensity is shown as avalue relative to the greatest emission intensity assumed to be 1. FIG.96 and FIG. 97 reveal that the light-emitting elements 11 and 12 eachblue green light due to [Ir(Mptz1-mp)₃], which is the emission centersubstance.

Next, the initial luminance is set at 1000 cd/m², these elements weredriven under a condition where the current density was constant, andchanges in luminance with respect to the driving time were examined.FIG. 98 shows normalized luminance versus time characteristics of thelight-emitting element 11, and FIG. 99 shows those of the light-emittingelement 12. From FIG. 98 and FIG. 99, it is found that each of thelight-emitting elements 11 and 12 has high reliability with a smallreduction in luminance with respect to driving time.

Thus, a light-emitting element, in which an emission center substanceemits blue phosphorescence and a carbazole derivative described inEmbodiment 1 is used as a host material or as a hole-transport material,can have high emission efficiency by efficient excitation for bluephosphorescence which is the light emission from the high tripletexcitation energy or by prevention of a loss due to energy transfer.This means that any of the carbazole derivatives described in Embodiment1 has very high triplet excitation energy.

Example 19 Synthesis Example 11

In this example is described a method of synthesizing3-(dibenzothiophen-4-yl)-9-[3-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: mDBTCzPA-II), which is one of the carbazole derivativesdescribed in Embodiment 1. A structure of mDBTCzPA-II is illustrated inthe following structural formula (13).

Step 1: Synthesis of 3-(Dibenzothiophen-4-yl)-9H-carbazole(abbreviation: DBTCz-II)

This was synthesized as in Step 1 in Example 1.

Step 2: Synthesis of3-(Dibenzothiophen-4-yl)-9-[3-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: mDBTCzPA-II)

In a 50-mL three-neck flask were put 1.2 g (3.0 mmol) of9-(3-bromophenyl)-10-phenylanthracene, 1.1 g (3.0 mmol) of3-(dibenzothiophen-4-yl)-9H-carbazole, and 0.87 g (9.1 mmol) of sodiumtert-butoxide. After the air in the flask was replaced with nitrogen, tothis mixture were added 20 mL of toluene and 0.2 mL oftri(tert-butyl)phosphine (a 10 wt % hexane solution). This mixture wasdegassed by being stirred while the pressure was reduced. After thedegassing, 87 mg (0.15 mmol) of bis(dibenzylideneacetone)palladium(0)was added to this mixture. This mixture was stirred at 110° C. for 5hours under a nitrogen stream. After the stirring, the obtained mixturewas suction-filtered through Celite (produced by Wako Pure ChemicalIndustries, Ltd., Catalog No. 531-16855), alumina, and Florisil(produced by Wako Pure Chemical Industries, Ltd., Catalog No.540-00135). The filtrate was concentrated to give a yellow solid. Theobtained solid was recrystallized from toluene. The obtained crystal waspurified by high performance liquid column chromatography (abbreviation:HPLC) (chloroform as the developing solvent). The obtained fraction wasconcentrated to give 1.5 g of a pale yellow solid in 72% yield. Thesynthesis scheme of Step 2 is illustrated in (b-11).

By a train sublimation method, the obtained pale yellow solid waspurified. The purification was conducted by heating of 1.0 g of the paleyellow solid at 300° C. under a pressure of 2.6 Pa with a flow rate ofargon gas of 5 mL/min. After the purification, 0.79 g of a white solidwas obtained in a yield of 79%.

The pale yellow solid after the above purification was subjected tonuclear magnetic resonance (NMR) spectroscopy. The measurement data areshown below.

¹H NMR (CDCl₃, 300 MHz): δ=7.30-7.52 (m, 10H), 7.55-7.68 (m, 7H),7.71-7.77 (m, 3H), 7.81-7.92 (m, 7H), 8.14-8.23 (m, 3H), 8.51 (d,J₁=0.90 Hz, 1H)

In addition, ¹H NMR charts are shown in FIGS. 100A and 100B. Note thatFIG. 100B is a chart where the range of from 7 ppm to 9 ppm in FIG. 100Ais enlarged. The measurement results showed that mDBTCzPA-II, which isthe carbazole derivative represented by the above structural formula,was obtained.

Further, an absorption and emission spectra of mDBTCzPA-II in a toluenesolution of mDBTCzPA-II are shown in FIG. 101A, and an absorption andemission spectra of a thin film of mDBTCzPA-II are shown in FIG. 101B.An ultraviolet-visible spectrophotometer (V-550, manufactured by JASCOCorporation) was used for the measurements of the absorption spectra. Inthe case of the toluene solution, the measurements were made with thetoluene solution of mDBTCzPA-II put in a quartz cell, and the absorptionspectrum obtained by subtraction of the absorption spectra of the quartzcell and toluene from the measured spectra is shown in the drawing. Inaddition, as for the absorption spectrum of the thin film, a sample wasprepared by evaporation of mDBTCzPA-II on a quartz substrate, and theabsorption spectrum obtained by subtraction of that of quartz from thespectrum of this sample is shown in the drawing. As in the measurementsof the absorption spectra, an ultraviolet-visible spectrophotometer(V-550, manufactured by JASCO Corporation) was used for the measurementsof the emission spectra. The emission spectrum was measured with thetoluene solution of mDBTCzPA-II put in a quartz cell, and the emissionspectrum of the thin film was measured with a sample prepared byevaporation of mDBTCzPA-II on a quartz substrate. Thus, it was foundthat the absorption peak wavelengths of mDBTCzPA-II in the toluenesolution of mDBTCzPA-II were around 396 nm, 375 nm, 354 nm, 336 nm and290 nm and the emission peak wavelengths thereof were around 412 nm and433 nm (at an excitation wavelength of 376 nm), and that the absorptionpeak wavelengths of the thin film of mDBTCzPA-II were around 402 nm, 381nm, 359 nm, 340 nm, 291 nm, 261 nm and 207 nm and the greatest emissionwavelength thereof was around 443 nm (at an excitation wavelength of 402nm).

Further, the ionization potential of mDBTCzPA-II in a thin film statewas measured by a photoelectron spectrometer (AC-2, manufactured byRiken Keiki, Co., Ltd.) in air. The obtained value of the ionizationpotential was converted to a negative value, so that the HOMO level ofmDBTCzPA-II was −5.77 eV. From the data of the absorption spectra of thethin film in FIG. 101B, the absorption edge of mDBTCzPA-II, which wasobtained from Tauc plot with an assumption of direct transition, was2.95 eV. Therefore, the optical energy gap of mDBTCzPA-II in the solidstate was estimated at 2.95 eV; from the values of the HOMO levelobtained above and this energy gap, the LUMO level of mDBTCzPA-II wasable to be estimated at −2.82 eV. It was thus found that mDBTCzPA-II hada wide energy gap of 2.95 eV in the solid state.

Further, the oxidation reaction characteristics of mDBTCzPA-II weremeasured. The oxidation reaction characteristics were examined by cyclicvoltammetry (CV) measurements. Note that an electrochemical analyzer(ALS model 600A or 600C, manufactured by BAS Inc.) was used for themeasurements.

For a solution for the CV measurements, dehydrated N,N-dimethylformamide(DMF, product of Sigma-Aldrich Inc., 99.8%, catalog No. 22705-6) wasused as a solvent, and tetra-n-butylammonium perchlorate (n-Bu₄NClO₄,product of Tokyo Chemical Industry Co., Ltd., catalog No. T0836), whichwas a supporting electrolyte, was dissolved in the solvent such that theconcentration thereof was 100 mmol/L. Further, the object to be measuredwas also dissolved in the solvent such that the concentration thereofwas 2 mmol/L. A platinum electrode (a PTE platinum electrode, product ofBAS Inc.) was used as a working electrode; a platinum electrode (a VC-3Pt counter electrode (5 cm), product of BAS Inc.) was used as anauxiliary electrode; and an Ag/Ag⁺ electrode (an RE5 nonaqueous solventreference electrode, product of BAS Inc.) was used as a referenceelectrode. Note that the measurements were conducted at room temperature(20° C. to 25° C.). The scan rates for the CV measurements wereuniformly set to 0.1 V/s.

In the measurements, scanning in which the potential of the workingelectrode with respect to the reference electrode was changed from −0.04V to 1.15 V and then changed from 1.15 V to −0.04 V was one cycle, and100 cycles were performed.

The measurement results revealed that mDBTCzPA-II showed propertieseffective against repetition of redox reactions between an oxidizedstate and a neutral state without a large variation in oxidation peakeven after the 100 cycles in the measurements.

Further, the HOMO level of mDBTCzPA-II was determined also bycalculation from the CV measurement results.

First, the potential energy of the reference electrode with respect tothe vacuum level used was found to be −4.94 eV, as determined in Example6. The oxidation peak potential E_(pa) of mDBTCzPA-II was 0.95 V. Inaddition, the reduction peak potential E_(pc) thereof was 0.83 V.Therefore, a half-wave potential (an intermediate potential betweenE_(pa) and E_(pc)) can be calculated at 0.89 V. This means thatmDBTCzPA-II is oxidized by an electric energy of 0.89 [V versus Ag/Ag⁺],and this energy corresponds to the HOMO level. Here, since the potentialenergy of the reference electrode, which was used in this example, withrespect to the vacuum level is −4.94 [eV] as described above, the HOMOlevel of mDBTCzPA-II was calculated as follows: −4.94−0.89=−5.83 [eV].

Example 20

In this example described is a light-emitting element in which3-(dibenzothiophen-4-yl)-9-[3-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: mDBTCzPA-II, a structural formula (13)), which is one ofthe carbazole derivatives represented by the general formula (G1), isused as a host material such that an emission center substance thatemits blue fluorescence is dispersed therein.

The molecular structures of organic compounds used in this example arerepresented by the structural formulae (13), (iv), and (iv) below.

In the element structure in FIG. 1A, an electron-injection layer isprovided between an electron-transport layer 114 and a second electrode104.

[Fabrication of Light-Emitting Element 13]

First, a glass substrate 101 over which indium tin oxide containingsilicon (ITSO) with a thickness of 110 nm was formed as a firstelectrode 102 was prepared. The periphery of a surface of the ITSO wascovered with a polyimide film so that an area of 2 mm×2 mm of thesurface was exposed. The electrode area was 2 mm×2 mm. As a pretreatmentfor forming the light-emitting element over the substrate, the surfaceof the substrate was washed with water and baked at 200° C. for onehour, and then a UV ozone treatment was performed for 370 seconds. Then,the substrate was transferred into a vacuum evaporation apparatus whosepressure was reduced to about 10⁻⁴ Pa, vacuum baking at 170° C. for 30minutes was performed in a heating chamber of the vacuum evaporationapparatus, and then the substrate was cooled down for about 30 minutes.

Then, the substrate was fixed on a holder provided in the vacuumevaporation apparatus such that the surface of the substrate 101provided with ITSO faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, a hole-injection layer 111 was formed by co-evaporation of9-[4-(9-phenylcarbazol-3-yl)]phenyl-10-phenylanthracene (abbreviation:PCzPA) represented by the above structural formula (v) andmolybdenum(VI) oxide such that the ratio of PCzPA:molybdenum(VI) oxidewas 2:1 (weight ratio). The thickness of was the layer was set to 50 nm.Note that the co-evaporation is an evaporation method in which aplurality of different substances is concurrently vaporized from therespective different evaporation sources.

Next, PCzPA was evaporated to a thickness of 10 nm, so that thehole-transport layer 112 was formed.

Further, the light-emitting layer 113 was formed on the hole-transportlayer 112 in such a way that3-(dibenzothiophen-4-yl)-9-[3-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: mDBTCzPA-II) represented by the above structural formula(13) andN,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenyl-pyrene-1,6-diamine(abbreviation: 1,6FLPAPm) represented by the structural formula (vi)were evaporated to form a 30-nm-thick film so that the ratio ofmDBTCzPA-II to 1,6FLPAPrn was 1:0.03 (weight ratio).

Next, on the light-emitting layer 113,tris(8-quinolinolato)aluminum(III) (abbreviation: Alq) represented bythe above structural formula (vii) was evaporated to a thickness of 10nm, and then bathophenanthroline (abbreviation: BPhen) represented bythe above structural formula (iv) was evaporated to a thickness of 15nm, so that the electron-transport layer 114 was formed. Then, lithiumfluoride was evaporated to a thickness of 1 nm on the electron-transportlayer 114, so that the electron-injection layer was formed. Lastly, analuminum film was formed to a thickness of 200 nm as the secondelectrode 104 functioning as a cathode, so that the light-emittingelement 13 was completed. Note that in the above evaporation processes,evaporation was all performed by a resistance heating method.

[Operation Characteristics of Light-Emitting Element 13]

The light-emitting element 13 thus obtained was sealed in a glove boxunder a nitrogen atmosphere without being exposed to the air. Then, theoperation characteristics of the light-emitting element were measured.Note that the measurements were carried out at room temperature (in anatmosphere kept at 25° C.).

FIG. 102 shows luminance current density characteristics of thelight-emitting element 13, FIG. 103 shows luminance versus voltagecharacteristics thereof, FIG. 104 shows current efficiency versusluminance characteristics thereof, and FIG. 105 shows current versusvoltage characteristics thereof. In FIG. 102, the vertical axisrepresents luminance (cd/m²), and the horizontal axis represents currentdensity (mA/cm²). In FIG. 103, the vertical axis represents luminance(cd/m²), and the horizontal axis represents voltage (V). In FIG. 104,the vertical axis represents current efficiency (cd/A), and thehorizontal axis represents luminance (cd/m²). In FIG. 105, the verticalaxis represents current (mA), and the horizontal axis represents voltage(V).

FIG. 104 reveals that the light-emitting elements in each of which thecarbazole derivative represented by the general formula (G1) is used asa host material of a light-emitting layer for emitting bluefluorescence, has favorable current efficiency versus luminancecharacteristics and high emission efficiency. This is because eachcarbazole derivative represented by the general formula (G1) has a wideenergy gap, and thus even a light-emitting substance that emits bluefluorescence and has a wide energy gap can be efficiently excited. Inaddition, FIG. 102 reveals that the light-emitting elements in each ofwhich the carbazole derivative represented by the general formula (G1)is used as a host material of a light-emitting layer for emitting bluefluorescence, has favorable luminance versus voltage characteristics andcan be driven with a low voltage. This indicates that each carbazolederivative represented by the general formula (G1) has an excellentcarrier-transport property.

FIG. 106 shows an emission spectrum when a current of 1 mA was made toflow in the fabricated light-emitting element 13. The emission intensityis shown as a value relative to the greatest emission intensity assumedto be 1. FIG. 106 reveals that the light-emitting element 13 emits bluelight due to 1,6FLPAPm, which is the emission center substance.

Next, the initial luminance is set at 5000 cd/m², the element was drivenunder a condition where the current density was constant, and changes inluminance with respect to the driving time were examined. FIG. 107 showsnormalized luminance versus time characteristics. From FIG. 107, it isfound that the light-emitting element 13 shows favorable characteristicsand has high reliability.

Example 21 Synthesis Example 12

In this example is described a method of synthesizing3-(dibenzofuran-4-yl)-9-[3-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: mDBFCzPA-II), which is one of the carbazole derivativesdescribed as the structural formula (14) in Embodiment 1. A structure ofmDBFCzPA-II is illustrated in the following structural formula.

Step 1: Synthesis of 3-(Dibenzofuran-4-yl)-9H-carbazole (abbreviation:DBFCz-II)

This was synthesized as in Step 1 in Example 2.

Step 2: Synthesis of3-(Dibenzofuran-4-yl)-9-[3-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: mDBFCzPA-II)

In a 100-mL three-neck flask were put 1.2 g (3.0 mmol) of9-(3-bromophenyl)-10-phenylanthracene, 1.0 g (3.0 mmol) of3-(dibenzofuran-4-yl)-9H-carbazole, and 0.87 g (9.1 mmol) of sodiumtert-butoxide. After the air in the flask was replaced with nitrogen, tothis mixture were added 20 mL of toluene and 0.2 mL oftri(tert-butyl)phosphine (a 10 wt % hexane solution). This mixture wasdegassed by being stirred while the pressure was reduced. After thedegassing, 87 mg (0.15 mmol) of bis(dibenzylideneacetone)palladium(0)was added to this mixture. This mixture was stirred at 110° C. for 6hours under a nitrogen stream. After the stirring, the obtained mixturewas suction-filtered through Celite (produced by Wako Pure ChemicalIndustries, Ltd., Catalog No. 531-16855), alumina, and Florisil(produced by Wako Pure Chemical Industries, Ltd., Catalog No.540-00135). The filtrate was concentrated to give a yellow solid. Theobtained solid was recrystallized from toluene to give 1.8 g of a whitesolid which was the object of the synthesis in 88% yield. The synthesisscheme of Step 2 is illustrated in (b-12).

By a train sublimation method, the obtained white solid was purified.The purification was conducted by heating of 1.2 g of the white solid at300° C. under a pressure of 2.6 Pa with a flow rate of argon gas of 5mL/min. After the purification, 1.1 g of a white solid was obtained in ayield of 89%.

The white solid after the above purification was subjected to nuclearmagnetic resonance (NMR) spectroscopy. The measurement data are shownbelow.

¹H NMR (CDCl₃, 300 MHz): δ=7.31-7.40 (m, 4H), 7.42-7.67 (m, 13H),7.70-7.81 (m, 5H), 7.85-7.92 (m, 4H), 7.95 (dd, J₁=1.5 Hz, J₂=7.8 Hz,1H), 7.99-8.03 (m, 2H), 8.24 (d, J₁=7.8 Hz, 1H), 8.65 (d, J₁=1.5 Hz, 1H)

In addition, ¹H NMR charts are shown in FIGS. 108A and 108B. Note thatFIG. 108B is a chart where the range of from 7 ppm to 9 ppm in FIG. 108Ais enlarged. The measurement results showed that mDBFCzPA-II, which isthe carbazole derivative represented by the above structural formula,was obtained.

Further, an absorption and emission spectra of mDBFCzPA-II in a toluenesolution of mDBFCzPA-II are shown in FIG. 109A, and an absorption andemission spectra of a thin film of mDBFCzPA-II are shown in FIG. 109B.An ultraviolet-visible spectrophotometer (V-550, manufactured by JASCOCorporation) was used for the measurements of the absorption spectra. Inthe case of the toluene solution, the measurements were made with thetoluene solution of mDBFCzPA-II put in a quartz cell, and the absorptionspectrum obtained by subtraction of the absorption spectra of the quartzcell and toluene from the measured spectra is shown in the drawing. Inaddition, as for the absorption spectrum of the thin film, a sample wasprepared by evaporation of mDBFCzPA-II on a quartz substrate, and theabsorption spectrum obtained by subtraction of that of quartz from thespectrum of this sample is shown in the drawing. As in the measurementsof the absorption spectra, an ultraviolet-visible spectrophotometer(V-550, manufactured by JASCO Corporation) was used for the measurementsof the emission spectra. The emission spectrum was measured with thetoluene solution of mDBFCzPA-II put in a quartz cell, and the emissionspectrum of the thin film was measured with a sample prepared byevaporation of mDBFCzPA-II on a quartz substrate. Thus, it was foundthat the absorption peak wavelengths of mDBFCzPA-II in the toluenesolution of mDBFCzPA-II were around 396 nm, 375 nm, 354 nm, 336 nm and290 nm and the emission peak wavelengths thereof were around 412 nm and433 nm (at an excitation wavelength of 375 nm), and that the absorptionpeak wavelengths of the thin film of mDBFCzPA-II were around 402 nm, 381nm, 359 nm, 340 nm, 291 nm, 261 nm and 207 nm and the greatest emissionwavelength thereof was around 443 nm (at an excitation wavelength of 402nm).

Further, the ionization potential of mDBFCzPA-II in a thin film statewas measured by a photoelectron spectrometer (AC-2, manufactured byRiken Keiki, Co., Ltd.) in air. The obtained value of the ionizationpotential was converted to a negative value, so that the HOMO level ofmDBFCzPA-II was −5.77 eV. From the data of the absorption spectra of thethin film in FIG. 109B, the absorption edge of mDBFCzPA-II, which wasobtained from Tauc plot with an assumption of direct transition, was2.95 eV. Therefore, the optical energy gap of mDBFCzPA-II in the solidstate was estimated at 2.95 eV; from the values of the HOMO levelobtained above and this energy gap, the LUMO level of mDBFCzPA-II wasable to be estimated at −2.82 eV. It was thus found that mDBFCzPA-II hada wide energy gap of 2.95 eV in the solid state.

Further, the oxidation reaction characteristics of mDBFCzPA-II weremeasured. The oxidation reaction characteristics were examined by cyclicvoltammetry (CV) measurements. Note that an electrochemical analyzer(ALS model 600A or 600C, manufactured by BAS Inc.) was used for themeasurements.

For a solution for the CV measurements, dehydrated N,N-dimethylformamide(DMF, product of Sigma-Aldrich Inc., 99.8%, catalog No. 22705-6) wasused as a solvent, and tetra-n-butylammonium perchlorate (n-Bu₄NClO₄,product of Tokyo Chemical Industry Co., Ltd., catalog No. T0836), whichwas a supporting electrolyte, was dissolved in the solvent such that theconcentration thereof was 100 mmol/L. Further, the object to be measuredwas also dissolved in the solvent such that the concentration thereofwas 2 mmol/L. A platinum electrode (a PTE platinum electrode, product ofBAS Inc.) was used as a working electrode; a platinum electrode (a VC-3Pt counter electrode (5 cm), product of BAS Inc.) was used as anauxiliary electrode; and an Ag/Ag⁺ electrode (an RE5 nonaqueous solventreference electrode, product of BAS Inc.) was used as a referenceelectrode. Note that the measurements were conducted at room temperature(20° C. to 25° C.). The scan rates for the CV measurements wereuniformly set to 0.1 V/s.

In the measurements, scanning in which the potential of the workingelectrode with respect to the reference electrode was changed from −0.04V to 1.15 V and then changed from 1.15 V to −0.04 V was one cycle, and100 cycles were performed.

The measurement results revealed that mDBFCzPA-II showed propertieseffective against repetition of redox reactions between an oxidizedstate and a neutral state without a large variation in oxidation peakeven after the 100 cycles in the measurements.

Further, the HOMO level of mDBFCzPA-II was determined also bycalculation from the CV measurement results.

First, the potential energy of the reference electrode with respect tothe vacuum level used was found to be −4.94 eV, as determined in Example6. The oxidation peak potential E_(pa) of mDBFCzPA-II was 0.95 V. Inaddition, the reduction peak potential E_(pc) thereof was 0.83 V.Therefore, a half-wave potential (an intermediate potential betweenE_(pa) and E_(pc)) can be calculated at 0.89 V. This means thatmDBFCzPA-II is oxidized by an electric energy of 0.89 [V versus Ag/Ag⁺],and this energy corresponds to the HOMO level. Here, since the potentialenergy of the reference electrode, which was used in this example, withrespect to the vacuum level is −4.94 [eV] as described above, the HOMOlevel of mDBFCzPA-II was calculated as follows: −4.94−0.89=−5.83 [eV].

Example 22

In this example described is a light-emitting element in which3-(dibenzofuran-4-yl)-9-[3-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: mDBFCzPA-II, a structural formula (14)), which is one ofthe carbazole derivatives represented by the general formula (G1), isused as a host material such that an emission center substance thatemits blue fluorescence is dispersed therein.

The molecular structures of organic compounds used in this example arerepresented by the structural formulae (14), (iv), and (iv) below.

In the element structure in FIG. 1A, an electron-injection layer isprovided between an electron-transport layer 114 and a second electrode104.

[Fabrication of Light-Emitting Element 14]

First, a glass substrate 101 over which indium tin oxide containingsilicon (ITSO) with a thickness of 110 nm was formed as a firstelectrode 102 was prepared. The periphery of a surface of the ITSO wascovered with a polyimide film so that an area of 2 mm×2 mm of thesurface was exposed. The electrode area was 2 mm×2 mm. As a pretreatmentfor forming the light-emitting element over the substrate, the surfaceof the substrate was washed with water and baked at 200° C. for onehour, and then a UV ozone treatment was performed for 370 seconds. Then,the substrate was transferred into a vacuum evaporation apparatus whosepressure was reduced to about 10−4 Pa, vacuum baking at 170° C. for 30minutes was performed in a heating chamber of the vacuum evaporationapparatus, and then the substrate was cooled down for about 30 minutes.

Then, the substrate was fixed on a holder provided in the vacuumevaporation apparatus such that the surface of the substrate 101provided with ITSO faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, a hole-injection layer 111 was formed by co-evaporation of9-[4-(9-phenylcarbazol-3-yl)]phenyl-10-phenylanthracene (abbreviation:PCzPA) represented by the above structural formula (v) andmolybdenum(VI) oxide such that the ratio of PCzPA:molybdenum(VI) oxidewas 2:1 (weight ratio). The thickness of was the layer was set to 50 nm.Note that the co-evaporation is an evaporation method in which aplurality of different substances is concurrently vaporized from therespective different evaporation sources.

Next, PCzPA was evaporated to a thickness of 10 nm, so that thehole-transport layer 112 was formed.

Further, the light-emitting layer 113 was formed on the hole-transportlayer 112 in such a way that3-(dibenzofuran-4-yl)-9-[3-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: mDBFCzPA-II) represented by the above structural formula(14) andN,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenyl-pyrene-1,6-diamine(abbreviation: 1,6FLPAPm) represented by the structural formula (vi)were evaporated to form a 30-nm-thick film so that the ratio ofmDBFCzPA-II to 1,6FLPAPrn was 1:0.05 (weight ratio).

Next, on the light-emitting layer 113,tris(8-quinolinolato)aluminum(III) (abbreviation: Alq) represented bythe above structural formula (vii) was evaporated to a thickness of 10nm, and then bathophenanthroline (abbreviation: BPhen) represented bythe above structural formula (iv) was evaporated to a thickness of 15nm, so that the electron-transport layer 114 was formed. Then, lithiumfluoride was evaporated to a thickness of 1 nm on the electron-transportlayer 114, so that the electron-injection layer was formed. Lastly, analuminum film was formed to a thickness of 200 nm as the secondelectrode 104 functioning as a cathode, so that the light-emittingelement 14 was completed. Note that in the above evaporation processes,evaporation was all performed by a resistance heating method.

[Operation Characteristics of Light-Emitting Element 14]

The light-emitting element 14 thus obtained was sealed in a glove boxunder a nitrogen atmosphere without being exposed to the air. Then, theoperation characteristics of the light-emitting element were measured.Note that the measurements were carried out at room temperature (in anatmosphere kept at 25° C.).

FIG. 110 shows luminance current density characteristics of thelight-emitting element 14, FIG. 111 shows luminance versus voltagecharacteristics thereof, FIG. 112 shows current efficiency versusluminance characteristics thereof, and FIG. 113 shows current versusvoltage characteristics thereof. In FIG. 110, the vertical axisrepresents luminance (cd/m²), and the horizontal axis represents currentdensity (mA/cm²). In FIG. 111, the vertical axis represents luminance(cd/m²), and the horizontal axis represents voltage (V). In FIG. 112,the vertical axis represents current efficiency (cd/A), and thehorizontal axis represents luminance (cd/m²). In FIG. 113, the verticalaxis represents current (mA), and the horizontal axis represents voltage(V).

FIG. 112 reveals that the light-emitting elements in each of which thecarbazole derivative represented by the general formula (G1) is used asa host material of a light-emitting layer for emitting bluefluorescence, has favorable luminance versus emission efficiencycharacteristics and high emission efficiency. This is because eachcarbazole derivative represented by the general formula (G1) has a wideenergy gap, and thus even a light-emitting substance that emits bluefluorescence and has a wide energy gap can be efficiently excited. Inaddition, FIG. 110 reveals that the light-emitting elements in each ofwhich the carbazole derivative represented by the general formula (G1)is used as a host material of a light-emitting layer for emitting bluefluorescence, has favorable luminance versus voltage characteristics andcan be driven with a low voltage. This indicates that each carbazolederivative represented by the general formula (G1) has an excellentcarrier-transport property.

FIG. 114 shows an emission spectrum when a current of 1 mA was made toflow in the fabricated light-emitting element 14. The emission intensityis shown as a value relative to the greatest emission intensity assumedto be 1. FIG. 114 reveals that the light-emitting element 14 emits bluelight due to 1,6FLPAPrn, which is the emission center substance.

Next, the initial luminance is set at 5000 cd/m², the element was drivenunder a condition where the current density was constant, and changes inluminance with respect to the driving time were examined. FIG. 115 showsnormalized luminance versus time characteristics. From FIG. 115, it isfound that the light-emitting element 14 shows favorable characteristicsand has high reliability.

Example 23 Synthesis Example 13

In this example is described a method of synthesizing3-(6-phenyldibenzothiophen-4-yl)-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: DBTCzPA-IV), which is one of the carbazole derivativesdescribed as the structural formula (15) in Embodiment 1. A structure ofDBTCzPA-IV is illustrated in the following structural formula.

Step 1: Synthesis of 3-(6-Phenyldibenzothiophen-4-yl)-9H-carbazole(abbreviation: DBTCz-IV)

In a 50-mL three-neck flask were put 1.0 g (4.1 mmol) of3-bromocarbazole, 1.2 g (4.1 mmol) of 6-phenyl-4-dibenzothienylboronicacid, and 62 mg (0.20 mmol) of tris(2-methylphenyl)phosphine. To thismixture were added 15 mL of toluene, 5 mL of ethanol, and 5 mL of a 2.0Maqueous sodium carbonate solution. This mixture was degassed by beingstirred while the pressure was reduced. To this mixture was added 9 mg(0.041 mmol) of palladium(II) acetate, and the mixture was stirred at80° C. for 3 hours under a nitrogen stream. After the stirring, theaqueous layer of this mixture was subjected to extraction with toluene,and the solution of the extract and the organic layer were combined andwashed with saturated brine. The organic layer was dried over magnesiumsulfate. This mixture was separated by gravity filtration, and thefiltrate was concentrated to give a solid. This solid was purified bysilica gel column chromatography (a developing solvent in which thetoluene/hexane ratio was 1:2 and then a developing solvent in which thetoluene/hexane ratio was 3:2). Addition of ethyl acetate/hexane to theobtained solid was followed by irradiation with ultrasonic waves, andthe solid was collected by suction filtration, so that 1.0 g of a whitesolid which was the object of the synthesis in 59% yield. The synthesisscheme of Step 1 is illustrated in (a-13).

The obtained white solid was subjected to nuclear magnetic resonance(NMR) spectroscopy. The measurement data are shown below.

¹H NMR (CDCl₃, 300 M Hz): δ=7.34-7.55 (m, 7H), 7.56 (d, J₁=4.2 Hz, 1H),7.58-7.64 (m, 3H), 7.68-7.72 (m, 2H), 7.78 (dd, J₁=1.8 Hz, J₂=8.4 Hz,1H), 8.10 (dd, J₁=0.90 Hz, J₂=1.8 Hz, 1H), 8.15 (s, 1H), 8.19-8.23 (m,2H), 8.36 (d, J₁=1.5 Hz, 1H)

Step 2: Synthesis of3-(6-Phenyldibenzothiophen-4-yl)-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: DBTCzPA-IV)

In a 50-mL three-neck flask were put 1.3 g (3.3 mmol) of9-(4-bromophenyl)-10-phenylanthracene, 1.0 g (2.4 mmol) of3-(6-phenyldibenzothiophen-4-yl)-9H-carbazole, and 0.95 g (9.9 mmol) ofsodium tert-butoxide. After the air in the flask was replaced withnitrogen, to this mixture were added 20 mL of toluene and 0.2 mL oftri(tert-butyl)phosphine (a 10 wt % hexane solution). This mixture wasdegassed by being stirred while the pressure was reduced. After thedegassing, 11 mg (0.18 mmol) of bis(dibenzylideneacetone)palladium(0)was added to this mixture. This mixture was stirred at 110° C. for 6hours under a nitrogen stream. After the stirring, the aqueous layer ofthis mixture was subjected to extraction with toluene, and the solutionof the extract and the organic layer were combined and washed withsaturated brine. The organic layer was dried over magnesium sulfate.This mixture was gravity-filtered, and the filtrate was concentrated togive a solid. The obtained solid was purified by silica gel columnchromatography (a developing solvent in which the toluene/hexane ratiowas 1:9 and then a developing solvent in which the toluene/hexane ratiowas 3:7). The obtained solid was recrystallized from toluene/hexane togive 1.4 g of a pale yellow solid which was the object of the synthesisin a yield of 80%. The synthesis scheme of Step 2 is illustrated in(b-13).

By a train sublimation method, 1.4 g of the obtained pale yellow solidwas purified. The purification was conducted by heating of the paleyellow solid at 360° C. under a pressure of 2.9 Pa with a flow rate ofargon gas of 5 mL/min. After the purification, 1.2 g of a pale yellowsolid was obtained in a yield of 86%.

The pale yellow solid after the above purification was subjected tonuclear magnetic resonance (NMR) spectroscopy. The measurement data areshown below.

¹H NMR (CDCl₃, 300 MHz): δ=7.34-7.49 (m, 9H), 7.51-7.54 (m, 3H), 7.57(t, J₁=1.5 Hz, 1H), 7.59-7.66 (m, 5H), 7.67-7.80 (m, 8H), 7.84-7.90 (m,5H), 8.22-8.25 (m, 3H), 8.49 (d, J₁=1.5 Hz, 1H).

In addition, ¹H NMR charts are shown in FIGS. 116A and 116B. Note thatFIG. 116B is a chart where the range of from 7 ppm to 9 ppm in FIG. 116Ais enlarged. The measurement results showed that DBTCzPA-IV, which isthe carbazole derivative represented by the above structural formula,was obtained.

Further, an absorption and emission spectra of DBTCzPA-IV in a toluenesolution of DBTCzPA-IV are shown in FIG. 117A, and an absorption andemission spectra of a thin film of DBTCzPA-IV are shown in FIG. 117B. Anultraviolet-visible spectrophotometer (V-550, manufactured by JASCOCorporation) was used for the measurements of the absorption spectra. Inthe case of the toluene solution, the measurements were made with thetoluene solution of DBTCzPA-IV put in a quartz cell, and the absorptionspectrum obtained by subtraction of the absorption spectra of the quartzcell and toluene from the measured spectra is shown in the drawing. Inaddition, as for the absorption spectrum of the thin film, a sample wasprepared by evaporation of DBTCzPA-IV on a quartz substrate, and theabsorption spectrum obtained by subtraction of that of quartz from thespectrum of this sample is shown in the drawing. As in the measurementsof the absorption spectra, an ultraviolet-visible spectrophotometer(V-550, manufactured by JASCO Corporation) was used for the measurementsof the emission spectra. The emission spectrum was measured with thetoluene solution of DBTCzPA-IV put in a quartz cell, and the emissionspectrum of the thin film was measured with a sample prepared byevaporation of DBTCzPA-IV on a quartz substrate. Thus, it was found thatthe absorption peak wavelengths of DBTCzPA-IV in the toluene solution ofDBTCzPA-IV were around 396 nm, 376 nm, 340 nm, and 281 nm and theemission peak wavelengths thereof were around 423 nm and 437 nm (at anexcitation wavelength of 376 nm), and that the absorption peakwavelengths of the thin film of DBTCzPA-IV were around 403 nm, 382 nm,356 nm, 345 nm, 296 nm, and 264 nm and the greatest emission wavelengththereof was around 443 nm (at an excitation wavelength of 403 nm).

Further, the ionization potential of DBTCzPA-IV in a thin film state wasmeasured by a photoelectron spectrometer (AC-2, manufactured by RikenKeiki, Co., Ltd.) in air. The obtained value of the ionization potentialwas converted to a negative value, so that the HOMO level of DBTCzPA-IVwas −5.80 eV. From the data of the absorption spectra of the thin filmin FIG. 117B, the absorption edge of DBTCzPA-IV, which was obtained fromTauc plot with an assumption of direct transition, was 2.93 eV.Therefore, the optical energy gap of DBTCzPA-IV in the solid state wasestimated at 2.93 eV; from the values of the HOMO level obtained aboveand this energy gap, the LUMO level of DBTCzPA-IV was able to beestimated at −2.87 eV. It was thus found that DBTCzPA-IV had a wideenergy gap of 2.93 eV in the solid state.

Further, the oxidation reaction characteristics of DBTCzPA-IV weremeasured. The oxidation reaction characteristics were examined by cyclicvoltammetry (CV) measurements. Note that an electrochemical analyzer(ALS model 600A or 600C, manufactured by BAS Inc.) was used for themeasurements.

For a solution for the CV measurements, dehydrated N,N-dimethylformamide(DMF, product of Sigma-Aldrich Inc., 99.8%, catalog No. 22705-6) wasused as a solvent, and tetra-n-butylammonium perchlorate (n-Bu₄NClO₄,product of Tokyo Chemical Industry Co., Ltd., catalog No. T0836), whichwas a supporting electrolyte, was dissolved in the solvent such that theconcentration thereof was 100 mmol/L. Further, the object to be measuredwas also dissolved in the solvent such that the concentration thereofwas 2 mmol/L. A platinum electrode (a PTE platinum electrode, product ofBAS Inc.) was used as a working electrode; a platinum electrode (a VC-3Pt counter electrode (5 cm), product of BAS Inc.) was used as anauxiliary electrode; and an Ag/Ag⁺ electrode (an RE5 nonaqueous solventreference electrode, product of BAS Inc.) was used as a referenceelectrode. Note that the measurements were conducted at room temperature(20° C. to 25° C.). The scan rates for the CV measurements wereuniformly set to 0.1 V/s.

In the measurements, scanning in which the potential of the workingelectrode with respect to the reference electrode was changed from −0.02V to 0.93 V and then changed from 0.93 V to −0.02 V was one cycle, and100 cycles were performed.

The measurement results revealed that DBTCzPA-IV showed propertieseffective against repetition of redox reactions between an oxidizedstate and a neutral state without a large variation in oxidation peakeven after the 100 cycles in the measurements.

Further, the HOMO level of DBTCzPA-IV was determined also by calculationfrom the CV measurement results.

First, the potential energy of the reference electrode with respect tothe vacuum level used was found to be −4.94 eV, as determined in Example6. The oxidation peak potential E_(pa) of DBTCzPA-IV was 0.89 V. Inaddition, the reduction peak potential E_(pc) thereof was 0.79 V.Therefore, a half-wave potential (an intermediate potential betweenE_(pa) and E_(pc)) can be calculated at 0.84 V. This means thatDBTCzPA-IV is oxidized by an electric energy of 0.84 [V versus Ag/Ag⁺],and this energy corresponds to the HOMO level. Here, since the potentialenergy of the reference electrode, which was used in this example, withrespect to the vacuum level is −4.94 [eV] as described above, the HOMOlevel of DBTCzPA-IV was calculated as follows: −4.94−0.84=−5.78.

Example 24

In this example described is a light-emitting element in which3-(6-phenyldibenzothiophen-4-yl)-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: DBTCzPA-IV, a structural formula (15)), which is one ofthe carbazole derivatives represented by the general formula (G1), isused as a host material such that an emission center substance thatemits blue fluorescence is dispersed therein.

The molecular structures of organic compounds used in this example arerepresented by the structural formulae (15), (iv), and (iv) below.

In the element structure in FIG. 1A, an electron-injection layer isprovided between an electron-transport layer 114 and a second electrode104.

[Fabrication of Light-Emitting Element 15]

First, a glass substrate 101 over which indium tin oxide containingsilicon (ITSO) with a thickness of 110 nm was formed as a firstelectrode 102 was prepared. The periphery of a surface of the ITSO wascovered with a polyimide film so that an area of 2 mm×2 mm of thesurface was exposed. The electrode area was 2 mm×2 mm. As a pretreatmentfor forming the light-emitting element over the substrate, the surfaceof the substrate was washed with water and baked at 200° C. for onehour, and then a UV ozone treatment was performed for 370 seconds. Then,the substrate was transferred into a vacuum evaporation apparatus whosepressure was reduced to about 10⁻⁴ Pa, vacuum baking at 170° C. for 30minutes was performed in a heating chamber of the vacuum evaporationapparatus, and then the substrate was cooled down for about 30 minutes.

Then, the substrate was fixed on a holder provided in the vacuumevaporation apparatus such that the surface of the substrate 101provided with ITSO faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, a hole-injection layer 111 was formed by co-evaporation of9-[4-(9-phenylcarbazol-3-yl)]phenyl-10-phenylanthracene (abbreviation:PCzPA) represented by the above structural formula (v) andmolybdenum(VI) oxide such that the ratio of PCzPA:molybdenum(VI) oxidewas 2:1 (weight ratio). The thickness of was the layer was set to 50 nm.Note that the co-evaporation is an evaporation method in which aplurality of different substances is concurrently vaporized from therespective different evaporation sources.

Next, PCzPA was evaporated to a thickness of 10 nm, so that thehole-transport layer 112 was formed.

Further, the light-emitting layer 113 was formed on the hole-transportlayer 112 such a way that3-(6-phenyldibenzothiophen-4-yl)-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: DBTCzPA-IV) represented by the above structural formula(15) andN,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenyl-pyrene-1,6-diamine(abbreviation: 1,6FLPAPrn) represented by the structural formula (vi)were evaporated to form a 30-nm-thick film so that the ratio ofDBTCzPA-IV to 1,6FLPAPrn was 1:0.03 (weight ratio).

Next, on the light-emitting layer 113,tris(8-quinolinolato)aluminum(III) (abbreviation: Alq) represented bythe above structural formula (vii) was evaporated to a thickness of 10nm, and then bathophenanthroline (abbreviation: BPhen) represented bythe above structural formula (iv) was evaporated to a thickness of 15nm, so that the electron-transport layer 114 was formed. Then, lithiumfluoride was evaporated to a thickness of 1 nm on the electron-transportlayer 114, so that the electron-injection layer was formed. Lastly, analuminum film was formed to a thickness of 200 nm as the secondelectrode 104 functioning as a cathode, so that the light-emittingelement 15 was completed. Note that in the above evaporation processes,evaporation was all performed by a resistance heating method.

[Operation Characteristics of Light-Emitting Element 15]

The light-emitting element 15 thus obtained was sealed in a glove boxunder a nitrogen atmosphere without being exposed to the air. Then, theoperation characteristics of the light-emitting element were measured.Note that the measurements were carried out at room temperature (in anatmosphere kept at 25° C.).

FIG. 118 shows luminance current density characteristics of thelight-emitting element 15, FIG. 119 shows luminance versus voltagecharacteristics thereof, FIG. 120 shows current efficiency versusluminance characteristics thereof, and FIG. 121 shows current versusvoltage characteristics thereof. In FIG. 118, the vertical axisrepresents luminance (cd/m²), and the horizontal axis represents currentdensity (mA/cm²). In FIG. 119, the vertical axis represents luminance(cd/m²), and the horizontal axis represents voltage (V). In FIG. 120,the vertical axis represents current efficiency (cd/A), and thehorizontal axis represents luminance (cd/m²). In FIG. 121, the verticalaxis represents current (mA), and the horizontal axis represents voltage(V).

FIG. 120 reveals that the light-emitting elements in each of which thecarbazole derivative represented by the general formula (G1) is used asa host material of a light-emitting layer for emitting bluefluorescence, has favorable current efficiency versus luminancecharacteristics and high emission efficiency. This is because eachcarbazole derivative represented by the general formula (G1) has a wideenergy gap, and thus even a light-emitting substance that emits bluefluorescence and has a wide energy gap can be efficiently excited. Inaddition, FIG. 119 reveals that the light-emitting elements in each ofwhich the carbazole derivative represented by the general formula (G1)is used as a host material of a light-emitting layer for emitting bluefluorescence, has favorable luminance versus voltage characteristics andcan be driven with a low voltage. This indicates that each carbazolederivative represented by the general formula (G1) has an excellentcarrier-transport property.

FIG. 122 shows an emission spectrum when a current of 1 mA was made toflow in the fabricated light-emitting element 15. The emission intensityis shown as a value relative to the greatest emission intensity assumedto be 1. FIG. 122 reveals that the light-emitting element 15 emits bluelight due to 1,6FLPAPm, which is the emission center substance.

Next, the initial luminance is set at 5000 cd/m², the element was drivenunder a condition where the current density was constant, and changes inluminance with respect to the driving time were examined. FIG. 123 showsnormalized luminance versus time characteristics. From FIG. 123, it isfound that the light-emitting element 15 shows favorable characteristicsand has high reliability.

Example 25 Synthesis Example 14

In this example is described a method of synthesizing3-(dibenzothiophen-4-yl)-9-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazole(abbreviation: 2DBTCzPPA-II), which is one of the carbazole derivativesdescribed as the structural formula (16) in Embodiment 1. A structure of2DBTCzPPA-II is illustrated in the following structural formula.

Step 1: Synthesis of 3-(Dibenzothiophen-4-yl)-9H-carbazole(abbreviation: DBTCz-II)

This was synthesized as in Step 1 in Synthesis Example 1.

Step 2: Synthesis of3-(Dibenzothiophen-4-yl)-9-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazole(abbreviation: 2DBTCzPPA-II)

In a 50-mL three-neck flask were put 1.3 g (2.7 mmol) of2-(4-bromophenyl)-9,10-diphenylanthracene, 0.93 g (2.7 mmol) of3-(dibenzothiophen-4-yl)-9H-carbazole, and 0.76 g (8.0 mmol) of sodiumtert-butoxide. After the air in the flask was replaced with nitrogen, tothis mixture were added 20 mL of toluene and 0.2 mL oftri(tert-butyl)phosphine (a 10 wt % hexane solution). This mixture wasdegassed by being stirred while the pressure was reduced. After thedegassing, 76 mg (0.13 mmol) of bis(dibenzylideneacetone)palladium(0)was added to this mixture. This mixture was stirred at 110° C. for 4hours under a nitrogen stream. After the stirring, the obtained mixturewas suction-filtered through Celite (produced by Wako Pure ChemicalIndustries, Ltd., Catalog No. 531-16855), alumina, and Florisil(produced by Wako Pure Chemical Industries, Ltd., Catalog No.540-00135), and the filtrate was concentrated to give a solid. Theobtained solid was purified by silica gel column chromatography (adeveloping solvent in which the hexane/toluene ratio was 5:1). Asuspension was formed by addition of toluene/hexane to the obtainedsolid, and the suspension was irradiated with ultrasonic wave. Then, asolid was collected by suction filtration, so that 1.2 g of a yellowsolid which was the object of the synthesis was obtained in a yield of61%. The synthesis scheme of Step 2 is illustrated in (b-14).

By a train sublimation method, the obtained yellow solid was purified.The purification was conducted by heating of 1.2 g of the yellow solidat 335° C. under a pressure of 2.6 Pa with a flow rate of argon gas of 5mL/min. After the purification, 1.01 g of a yellow solid was obtained ina yield of 83%.

The yellow solid after the above purification was subjected to nuclearmagnetic resonance (NMR) spectroscopy. The measurement data are shownbelow.

¹H NMR (CDCl₃, 300 MHz): δ=7.29-7.39 (m, 3H), 7.41-7.51 (m, 4H),7.52-7.75 (m, 18H), 7.78-7.88 (m, 5H), 8.03 (d, J₁=1.5 Hz, 1H),8.15-8.23 (m, 3H), 8.51 (d, J₁=0.90 Hz, 1H).

In addition, ¹H NMR charts are shown in FIGS. 124A and 124B. Note thatFIG. 124B is a chart where the range of from 7 ppm to 9 ppm in FIG. 124Ais enlarged. The measurement results showed that 2DBTCzPPA-II, which isthe carbazole derivative represented by the above structural formula,was obtained.

Further, an absorption and emission spectra of 2DBTCzPPA-II in a toluenesolution of 2DBTCzPPA-II are shown in FIG. 125A, and an absorption andemission spectra of a thin film of 2DBTCzPPA-II are shown in FIG. 125B.An ultraviolet-visible spectrophotometer (V-550, manufactured by JASCOCorporation) was used for the measurements of the absorption spectra. Inthe case of the toluene solution, the measurements were made with thetoluene solution of 2DBTCzPPA-II put in a quartz cell, and theabsorption spectrum obtained by subtraction of the absorption spectra ofthe quartz cell and toluene from the measured spectra is shown in thedrawing. In addition, as for the absorption spectrum of the thin film, asample was prepared by evaporation of 2DBTCzPPA-II on a quartzsubstrate, and the absorption spectrum obtained by subtraction of thatof quartz from the spectrum of this sample is shown in the drawing. Asin the measurements of the absorption spectra, an ultraviolet-visiblespectrophotometer (V-550, manufactured by JASCO Corporation) was usedfor the measurements of the emission spectra. The emission spectrum wasmeasured with the toluene solution of 2DBTCzPPA-II put in a quartz cell,and the emission spectrum of the thin film was measured with a sampleprepared by evaporation of 2DBTCzPPA-II on a quartz substrate. Thus, itwas found that the absorption peak wavelengths of 2DBTCzPPA-II in thetoluene solution of 2DBTCzPPA-II were around 404 nm, 382 nm, 336 nm, and285 nm and the emission peak wavelengths thereof were around 483 nm, 452nm, and 427 nm (at an excitation wavelength of 387 nm), and that theabsorption peak wavelengths of the thin film of 2DBTCzPPA-II were around415 nm, 393 nm, 346 nm, 291 nm, and 244 nm and the emission peakwavelengths thereof were around 461 nm and 442 nm (at an excitationwavelength of 415 nm).

Further, the ionization potential of 2DBTCzPPA-II in a thin film statewas measured by a photoelectron spectrometer (AC-2, manufactured byRiken Keiki, Co., Ltd.) in air. The obtained value of the ionizationpotential was converted to a negative value, so that the HOMO level of2DBTCzPPA-II was −5.70 eV. From the data of the absorption spectra ofthe thin film in FIG. 125B, the absorption edge of 2DBTCzPPA-II, whichwas obtained from Tauc plot with an assumption of direct transition, was2.81 eV. Therefore, the optical energy gap of 2DBTCzPPA-II in the solidstate was estimated at 2.81 eV; from the values of the HOMO levelobtained above and this energy gap, the LUMO level of 2DBTCzPPA-II wasable to be estimated at −2.89 eV. It was thus found that 2DBTCzPPA-IIhad a wide energy gap of 2.81 eV in the solid state.

Further, the oxidation reaction characteristics of 2DBTCzPPA-II weremeasured. The oxidation reaction characteristics were examined by cyclicvoltammetry (CV) measurements. Note that an electrochemical analyzer(ALS model 600A or 600C, manufactured by BAS Inc.) was used for themeasurements.

For a solution for the CV measurements, dehydrated N,N-dimethylformamide(DMF, product of Sigma-Aldrich Inc., 99.8%, catalog No. 22705-6) wasused as a solvent, and tetra-n-butylammonium perchlorate (n-Bu₄NClO₄,product of Tokyo Chemical Industry Co., Ltd., catalog No. T0836), whichwas a supporting electrolyte, was dissolved in the solvent such that theconcentration thereof was 100 mmol/L. Further, the object to be measuredwas also dissolved in the solvent such that the concentration thereofwas 2 mmol/L. A platinum electrode (a PTE platinum electrode, product ofBAS Inc.) was used as a working electrode; a platinum electrode (a VC-3Pt counter electrode (5 cm), product of BAS Inc.) was used as anauxiliary electrode; and an Ag/Ag⁺ electrode (an RE5 nonaqueous solventreference electrode, product of BAS Inc.) was used as a referenceelectrode. Note that the measurements were conducted at room temperature(20° C. to 25° C.). The scan rates for the CV measurements wereuniformly set to 0.1 V/s.

In the measurements, scanning in which the potential of the workingelectrode with respect to the reference electrode was changed from 0.31V to 0.92 V and then changed from 0.92 V to 0.31 V was one cycle, and100 cycles were performed.

The measurement results revealed that 2DBTCzPPA-II showed propertieseffective against repetition of redox reactions between an oxidizedstate and a neutral state without a large variation in oxidation peakeven after the 100 cycles in the measurements.

Further, the HOMO level of 2DBTCzPPA-II was determined also bycalculation from the CV measurement results.

First, the potential energy of the reference electrode with respect tothe vacuum level used was found to be −4.94 eV, as determined in Example6. The oxidation peak potential E_(pa) of 2DBTCzPPA-II was 0.88 V. Inaddition, the reduction peak potential E_(pc) thereof was 0.80 V.Therefore, a half-wave potential (an intermediate potential betweenE_(pa) and E_(pc)) can be calculated at 0.84 V. This means that2DBTCzPPA-II is oxidized by an electric energy of 0.84 [V versusAg/Ag⁺], and this energy corresponds to the HOMO level. Here, since thepotential energy of the reference electrode, which was used in thisexample, with respect to the vacuum level is −4.94 [eV] as describedabove, the HOMO level of 2DBTCzPPA-II was calculated as follows:−4.94−0.84=−5.78. [eV].

Example 26

In this example described is a light-emitting element in which3-(dibenzothiophen-4-yl)-9-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazole(abbreviation: 2DBTCzPPA-II, a structural formula (16)), which is one ofthe carbazole derivatives represented by the general formula (G1), isused as a host material such that an emission center substance thatemits blue fluorescence is dispersed therein.

The molecular structures of organic compounds used in this example arerepresented by the structural formulae (16), (iv), and (iv) below.

In the element structure in FIG. 1A, an electron-injection layer isprovided between an electron-transport layer 114 and a second electrode104.

[Fabrication of Light-Emitting Element 16]

First, a glass substrate 101 over which indium tin oxide containingsilicon (ITSO) with a thickness of 110 nm was formed as a firstelectrode 102 was prepared. The periphery of a surface of the ITSO wascovered with a polyimide film so that an area of 2 mm×2 mm of thesurface was exposed. The electrode area was 2 mm×2 mm. As a pretreatmentfor forming the light-emitting element over the substrate, the surfaceof the substrate was washed with water and baked at 200° C. for onehour, and then a UV ozone treatment was performed for 370 seconds. Then,the substrate was transferred into a vacuum evaporation apparatus whosepressure was reduced to about 10⁻⁴ Pa, vacuum baking at 170° C. for 30minutes was performed in a heating chamber of the vacuum evaporationapparatus, and then the substrate was cooled down for about 30 minutes.

Then, the substrate was fixed on a holder provided in the vacuumevaporation apparatus such that the surface of the substrate 101provided with ITSO faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, a hole-injection layer 111 was formed by co-evaporation of9-[4-(9-phenylcarbazol-3-yl)]phenyl-10-phenylanthracene (abbreviation:PCzPA) represented by the above structural formula (v) andmolybdenum(VI) oxide such that the ratio of PCzPA:molybdenum(VI) oxidewas 2:1 (weight ratio). The thickness of was the layer was set to 50 nm.Note that the co-evaporation is an evaporation method in which aplurality of different substances is concurrently vaporized from therespective different evaporation sources.

Next, PCzPA was evaporated to a thickness of 10 nm, so that thehole-transport layer 112 was formed.

Further, the light-emitting layer 113 was foamed on the hole-transportlayer 112 in such a way that3-(dibenzothiophen-4-yl)-9-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazole(abbreviation: 2DBTCzPPA-II) represented by the above structural formula(16) andN,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenyl-pyrene-1,6-diamine(abbreviation: 1,6FLPAPrn) represented by the structural formula (vi)were evaporated to form a 30-nm-thick film so that the ratio of2DBTCzPPA-II to 1,6FLPAPrn was 1:0.05 (weight ratio).

Next, on the light-emitting layer 113,tris(8-quinolinolato)aluminum(III) (abbreviation: Alq) represented bythe above structural formula (vii) was evaporated to a thickness of 10nm, and then bathophenanthroline (abbreviation: BPhen) represented bythe above structural formula (iv) was evaporated to a thickness of 15nm, so that the electron-transport layer 114 was formed. Then, lithiumfluoride was evaporated to a thickness of 1 nm on the electron-transportlayer 114, so that the electron-injection layer was formed. Lastly, analuminum film was formed to a thickness of 200 nm as the secondelectrode 104 functioning as a cathode, so that the light-emittingelement 16 was completed. Note that in the above evaporation processes,evaporation was all performed by a resistance heating method.

[Operation Characteristics of Light-Emitting Element 16]

The light-emitting element 16 thus obtained was sealed in a glove boxunder a nitrogen atmosphere without being exposed to the air. Then, theoperation characteristics of the light-emitting element were measured.Note that the measurements were carried out at room temperature (in anatmosphere kept at 25° C.).

FIG. 126 shows luminance current density characteristics of thelight-emitting element 16, FIG. 127 shows luminance versus voltagecharacteristics thereof, FIG. 128 shows current efficiency versusluminance characteristics thereof, and FIG. 129 shows current versusvoltage characteristics thereof. In FIG. 126, the vertical axisrepresents luminance (cd/m²), and the horizontal axis represents currentdensity (mA/cm²). In FIG. 127, the vertical axis represents luminance(cd/m²), and the horizontal axis represents voltage (V). In FIG. 128,the vertical axis represents current efficiency (cd/A), and thehorizontal axis represents luminance (cd/m²). In FIG. 129, the verticalaxis represents current (mA), and the horizontal axis represents voltage(V).

FIG. 128 reveals that the light-emitting elements in each of which thecarbazole derivative represented by the general formula (G1) is used asa host material of a light-emitting layer for emitting bluefluorescence, has favorable current efficiency versus luminancecharacteristics and high emission efficiency. This is because eachcarbazole derivative represented by the general formula (G1) has a wideenergy gap, and thus even a light-emitting substance that emits bluefluorescence and has a wide energy gap can be efficiently excited. Inaddition, FIG. 127 reveals that the light-emitting elements in each ofwhich the carbazole derivative represented by the general formula (G1)is used as a host material of a light-emitting layer for emitting bluefluorescence, has favorable luminance versus voltage characteristics andcan be driven with a low voltage. This indicates that each carbazolederivative represented by the general formula (G1) has an excellentcarrier-transport property.

FIG. 130 shows an emission spectrum when a current of 1 mA was made toflow in the fabricated light-emitting element 16. The emission intensityis shown as a value relative to the greatest emission intensity assumedto be 1. FIG. 130 reveals that the light-emitting element 16 emits bluelight due to 1,6FLPAPrn, which is the emission center substance.

Next, the initial luminance is set at 1000 cd/m², the element was drivenunder a condition where the current density was constant, and changes inluminance with respect to the driving time were examined. FIG. 131 showsnormalized luminance versus time characteristics. From FIG. 131, it isfound that the light-emitting element 16 shows favorable characteristicsand has high reliability.

Example 27 Synthesis Example 15

In this example is described a method of synthesizing3-(dibenzofuran-4-yl)-9-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazole(abbreviation: 2DBFCzPPA-II), which is one of the carbazole derivativesdescribed as the structural formula (17) in Embodiment 1. A structure of2DBFCzPPA-II is illustrated in the following structural formula.

Step 1: Synthesis of 3-(Dibenzofuran-4-yl)-9H-carbazole (abbreviation:DBFCz-II)

This was synthesized as in Step 1 in Synthesis Example 2.

Step 2: Synthesis of3-(Dibenzofuran-4-yl)-9-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazole(abbreviation: 2DBFCzPPA-II)

In a 50-mL three-neck flask were put 1.3 g (2.7 mmol) of2-(4-bromophenyl)-9,10-diphenylanthracene, 0.88 g (2.7 mmol) of3-(dibenzofuran-4-yl)-9H-carbazole, and 0.76 g (8.0 mmol) of sodiumtert-butoxide. After the air in the flask was replaced with nitrogen, tothis mixture were added 20 mL of toluene and 0.2 mL oftri(tert-butyl)phosphine (a 10 wt % hexane solution). This mixture wasdegassed by being stirred while the pressure was reduced. After thedegassing, 76 mg (0.13 mmol) of bis(dibenzylideneacetone)palladium(0)was added to this mixture. This mixture was stirred at 110° C. for 4hours under a nitrogen stream. After the stirring, the obtained mixturewas suction-filtered through Celite (produced by Wako Pure ChemicalIndustries, Ltd., Catalog No. 531-16855), alumina, and Florisil(produced by Wako Pure Chemical Industries, Ltd., Catalog No.540-00135), and the filtrate was concentrated to give a solid. Thissolid was purified by silica gel column chromatography (a developingsolvent in which the hexane/toluene ratio was 5:1). This solid waspurified by high performance liquid column chromatography (abbreviation:HPLC) (chloroform as the developing solvent). The obtained fraction wasconcentrated to give 1.4 g of a yellow solid which was the object of thesynthesis in 71% yield. The synthesis scheme of Step 2 is illustrated in(b-15).

By a train sublimation method, the obtained yellow solid was purified.The purification was conducted by heating of 0.90 g of the yellow solidat 360° C. under a pressure of 2.6 Pa with a flow rate of argon gas of 5mL/min. After the purification, 0.73 g of a yellow solid was obtained ina yield of 81%.

The yellow solid after the above purification was subjected to nuclearmagnetic resonance (NMR) spectroscopy. The measurement data are shownbelow.

¹H NMR (CDCl₃, 300 MHz): δ=7.30-7.42 (m, 4H), 7.45-7.52 (m, 4H),7.53-7.75 (m, 18H), 7.78-7.88 (m, 3H), 7.93-8.03 (m, 4H), 8.24 (d,J₁=7.5 Hz, 1H), 8.66 (d, J₁=1.5 Hz, 1H).

In addition, ¹H NMR charts are shown in FIGS. 132A and 132B. Note thatFIG. 132B is a chart where the range of from 7 ppm to 9 ppm in FIG. 132Ais enlarged. The measurement results showed that 2DBFCzPPA-II, which isthe carbazole derivative represented by the above structural formula,was obtained.

Further, an absorption and emission spectra of 2DBFCzPPA-II in a toluenesolution of 2DBFCzPPA-II are shown in FIG. 133A, and an absorption andemission spectra of a thin film of 2DBFCzPPA-II are shown in FIG. 133B.An ultraviolet-visible spectrophotometer (V-550, manufactured by JASCOCorporation) was used for the measurements of the absorption spectra. Inthe case of the toluene solution, the measurements were made with thetoluene solution of 2DBFCzPPA-II put in a quartz cell, and theabsorption spectrum obtained by subtraction of the absorption spectra ofthe quartz cell and toluene from the measured spectra is shown in thedrawing. In addition, as for the absorption spectrum of the thin film, asample was prepared by evaporation of 2DBFCzPPA-II on a quartzsubstrate, and the absorption spectrum obtained by subtraction of thatof quartz from the spectrum of this sample is shown in the drawing. Asin the measurements of the absorption spectra, an ultraviolet-visiblespectrophotometer (V-550, manufactured by JASCO Corporation) was usedfor the measurements of the emission spectra. The emission spectrum wasmeasured with the toluene solution of 2DBFCzPPA-II put in a quartz cell,and the emission spectrum of the thin film was measured with a sampleprepared by evaporation of 2DBFCzPPA-II on a quartz substrate. Thus, itwas found that the absorption peak wavelengths of 2DBFCzPPA-II in thetoluene solution of 2DBFCzPPA-II were around 403 nm, 381 nm, 336 nm and284 nm and the emission peak wavelengths thereof were around 453 nm and427 nm (at an excitation wavelength of 387 nm), and that the absorptionpeak wavelengths of the thin film of 2DBFCzPPA-II were around 415 nm,392 nm, 347 nm, 291 nm and 254 nm and the greatest emission wavelengthsthereof were around 461 nm and 443 nm (at an excitation wavelength of415 nm).

Further, the ionization potential of 2DBFCzPPA-II in a thin film statewas measured by a photoelectron spectrometer (AC-2, manufactured byRiken Keiki, Co., Ltd.) in air. The obtained value of the ionizationpotential was converted to a negative value, so that the HOMO level of2DBFCzPPA-II was −5.68 eV. From the data of the absorption spectra ofthe thin film in FIG. 133B, the absorption edge of 2DBFCzPPA-II, whichwas obtained from Tauc plot with an assumption of direct transition, was2.81 eV. Therefore, the optical energy gap of 2DBFCzPPA-II in the solidstate was estimated at 2.81 eV; from the values of the HOMO levelobtained above and this energy gap, the LUMO level of 2DBFCzPPA-II wasable to be estimated at −2.87 eV. It was thus found that 2DBFCzPPA-IIhad a wide energy gap of 2.81 eV in the solid state.

Further, the oxidation reaction characteristics of 2DBFCzPPA-II weremeasured. The oxidation reaction characteristics were examined by cyclicvoltammetry (CV) measurements. Note that an electrochemical analyzer(ALS model 600A or 600C, manufactured by BAS Inc.) was used for themeasurements.

For a solution for the CV measurements, dehydrated N,N-dimethylformamide(DMF, product of Sigma-Aldrich Inc., 99.8%, catalog No. 22705-6) wasused as a solvent, and tetra-n-butylammonium perchlorate (n-Bu₄NClO₄,product of Tokyo Chemical Industry Co., Ltd., catalog No. T0836), whichwas a supporting electrolyte, was dissolved in the solvent such that theconcentration thereof was 100 mmol/L. Further, the object to be measuredwas also dissolved in the solvent such that the concentration thereofwas 2 mmol/L. A platinum electrode (a PTE platinum electrode, product ofBAS Inc.) was used as a working electrode; a platinum electrode (a VC-3Pt counter electrode (5 cm), product of BAS Inc.) was used as anauxiliary electrode; and an Ag/Ag⁺ electrode (an RE5 nonaqueous solventreference electrode, product of BAS Inc.) was used as a referenceelectrode. Note that the measurements were conducted at room temperature(20° C. to 25° C.). The scan rates for the CV measurements wereuniformly set to 0.1 V/s.

In the measurements, scanning in which the potential of the workingelectrode with respect to the reference electrode was changed from 0.27V to 0.90 V and then changed from 0.90 V to 0.26 V was one cycle, and100 cycles were performed.

The measurement results revealed that 2DBFCzPPA-II showed propertieseffective against repetition of redox reactions between an oxidizedstate and a neutral state without a large variation in oxidation peakeven after the 100 cycles in the measurements.

Further, the HOMO level of 2DBFCzPPA-II was determined also bycalculation from the CV measurement results.

First, the potential energy of the reference electrode with respect tothe vacuum level used was found to be −4.94 eV, as determined in Example6. The oxidation peak potential E_(pa) of 2DBFCzPPA-II was 0.89 V. Inaddition, the reduction peak potential E_(pc) thereof was 0.75 V.Therefore, a half-wave potential (an intermediate potential betweenE_(pa) and E_(pc)) can be calculated at 0.82 V. This means that2DBFCzPPA-II is oxidized by an electric energy of 0.82 [V versusAg/Ag⁺], and this energy corresponds to the HOMO level. Here, since thepotential energy of the reference electrode, which was used in thisexample, with respect to the vacuum level is −4.94 [eV] as describedabove, the HOMO level of 2DBFCzPPA-II was calculated as follows:−4.94−0.82=−5.76 [eV].

Example 28

In this example described is a light-emitting element in which3-(dibenzofuran-4-yl)-9-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazole(abbreviation: 2DBFCzPPA-II, a structural formula (17)), which is one ofthe carbazole derivatives represented by the general formula (G1), isused as a host material such that an emission center substance thatemits blue fluorescence is dispersed therein.

The molecular structures of organic compounds used in this example arerepresented by the structural formulae (17), (iv), and (iv) below.

In the element structure in FIG. 1A, an electron-injection layer isprovided between an electron-transport layer 114 and a second electrode104.

[Fabrication of Light-Emitting Element 17]

First, a glass substrate 101 over which indium tin oxide containingsilicon (ITSO) with a thickness of 110 nm was formed as a firstelectrode 102 was prepared. The periphery of a surface of the ITSO wascovered with a polyimide film so that an area of 2 mm×2 mm of thesurface was exposed. The electrode area was 2 mm×2 mm. As a pretreatmentfor forming the light-emitting element over the substrate, the surfaceof the substrate was washed with water and baked at 200° C. for onehour, and then a UV ozone treatment was performed for 370 seconds. Then,the substrate was transferred into a vacuum evaporation apparatus whosepressure was reduced to about 10⁻⁴ Pa, vacuum baking at 170° C. for 30minutes was performed in a heating chamber of the vacuum evaporationapparatus, and then the substrate was cooled down for about 30 minutes.

Then, the substrate was fixed on a holder provided in the vacuumevaporation apparatus such that the surface of the substrate 101provided with ITSO faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, a hole-injection layer 111 was formed by co-evaporation of9-[4-(9-phenylcarbazol-3-yl)]phenyl-10-phenylanthracene (abbreviation:PCzPA) represented by the above structural formula (v) andmolybdenum(VI) oxide such that the ratio of PCzPA:molybdenum(VI) oxidewas 2:1 (weight ratio). The thickness of was the layer was set to 50 nm.Note that the co-evaporation is an evaporation method in which aplurality of different substances is concurrently vaporized from therespective different evaporation sources.

Next, PCzPA was evaporated to a thickness of 10 nm, so that thehole-transport layer 112 was formed.

Further, the light-emitting layer 113 was formed on the hole-transportlayer 112 in such a way that3-(dibenzofuran-4-yl)-9-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazole(abbreviation: 2DBFCzPPA-II) represented by the above structural formula(17) andN,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenyl-pyrene-1,6-diamine(abbreviation: 1,6FLPAPm) represented by the structural formula (vi)were evaporated to form a 30-nm-thick film so that the ratio of2DBFCzPPA-II to 1,6FLPAPm was 1:0.05 (weight ratio).

Next, on the light-emitting layer 113,tris(8-quinolinolato)aluminum(III) (abbreviation: Alq) represented bythe above structural formula (vii) was evaporated to a thickness of 10nm, and then bathophenanthroline (abbreviation: BPhen) represented bythe above structural formula (iv) was evaporated to a thickness of 15nm, so that the electron-transport layer 114 was formed. Then, lithiumfluoride was evaporated to a thickness of 1 nm on the electron-transportlayer 114, so that the electron-injection layer was formed. Lastly, analuminum film was formed to a thickness of 200 nm as the secondelectrode 104 functioning as a cathode, so that the light-emittingelement 17 was completed. Note that in the above evaporation processes,evaporation was all performed by a resistance heating method.

[Operation Characteristics of Light-Emitting Element 17]

The light-emitting element 17 thus obtained was sealed in a glove boxunder a nitrogen atmosphere without being exposed to the air. Then, theoperation characteristics of the light-emitting element were measured.Note that the measurements were carried out at room temperature (in anatmosphere kept at 25° C.).

FIG. 134 shows luminance current density characteristics of thelight-emitting element 17, FIG. 135 shows luminance versus voltagecharacteristics thereof, FIG. 136 shows current efficiency versusluminance characteristics thereof, and FIG. 137 shows current versusvoltage characteristics thereof. In FIG. 134, the vertical axisrepresents luminance (cd/m²), and the horizontal axis represents currentdensity (mA/cm²). In FIG. 135, the vertical axis represents luminance(cd/m²), and the horizontal axis represents voltage (V). In FIG. 136,the vertical axis represents current efficiency (cd/A), and thehorizontal axis represents luminance (cd/m²). In FIG. 137, the verticalaxis represents current (mA), and the horizontal axis represents voltage(V).

FIG. 136 reveals that the light-emitting elements in each of which thecarbazole derivative represented by the general formula (G1) is used asa host material of a light-emitting layer for emitting bluefluorescence, has favorable current efficiency versus luminancecharacteristics and high emission efficiency. This is because eachcarbazole derivative represented by the general formula (G1) has a wideenergy gap, and thus even a light-emitting substance that emits bluefluorescence and has a wide energy gap can be efficiently excited. Inaddition, FIG. 135 reveals that the light-emitting elements in each ofwhich the carbazole derivative represented by the general formula (G1)is used as a host material of a light-emitting layer for emitting bluefluorescence, has favorable luminance versus voltage characteristics andcan be driven with a low voltage. This indicates that each carbazolederivative represented by the general formula (G1) has an excellentcarrier-transport property.

FIG. 138 shows an emission spectrum when a current of 1 mA was made toflow in the fabricated light-emitting element 17. The emission intensityis shown as a value relative to the greatest emission intensity assumedto be 1. FIG. 138 reveals that the light-emitting element 17 emits bluelight due to 1,6FLPAPm, which is the emission center substance.

Next, the initial luminance is set at 1000 cd/m², the element was drivenunder a condition where the current density was constant, and changes inluminance with respect to the driving time were examined. FIG. 139 showsnormalized luminance versus time characteristics. From FIG. 139, it isfound that the light-emitting element 17 shows favorable characteristicsand has high reliability.

Example 29 Synthesis Example 16

In this example is described a method of synthesizing3-(dibenzothiophen-4-yl)-9-[3-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazole(abbreviation: 2mDBTCzPPA-II), which is one of the carbazole derivativesdescribed as the structural formula (18) in Embodiment 1. A structure of2mDBTCzPPA-II is illustrated in the following structural formula.

Step 1: Synthesis of 3-(Dibenzothiophen-4-yl)-9H-carbazole(abbreviation: DBTCz-II)

This was synthesized as in Step 1 in Synthesis Example 1.

Step 2: Synthesis of3-(Dibenzothiophen-4-yl)-9-[3-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazole(abbreviation: 2mDBTCzPPA-II)

In a 100-mL three-neck flask were put 1.0 g (2.1 mmol) of2-(3-bromophenyl)-9,10-diphenylanthracene, 0.72 g (2.1 mmol) of3-(dibenzothiophen-4-yl)-9H-carbazole, and 0.59 g (6.2 mmol) of sodiumtert-butoxide. After the air in the flask was replaced with nitrogen, tothis mixture were added 20 mL of toluene and 0.2 mL oftri(tert-butyl)phosphine (a 10 wt % hexane solution). This mixture wasdegassed by being stirred while the pressure was reduced. After thedegassing, 59 mg (0.10 mmol) of bis(dibenzylideneacetone)palladium(0)was added to this mixture. This mixture was stirred at 110° C. for 5hours under a nitrogen stream. After the stirring, the obtained mixturewas suction-filtered through Celite (produced by Wako Pure ChemicalIndustries, Ltd., Catalog No. 531-16855), alumina, and Florisil(produced by Wako Pure Chemical Industries, Ltd., Catalog No.540-00135). The filtrate was concentrated to give a yellow solid. Thissolid was purified by silica gel column chromatography (a developingsolvent in which the hexane/toluene ratio was 5:1). The obtained solidwas recrystallized from toluene/hexane to give 1.1 g of a yellow solidin 70% yield. The synthesis scheme of Step 2 is illustrated in (b-16).

By a train sublimation method, the obtained yellow solid was purified.The purification was conducted by heating of 1.1 g of the yellow solidat 330° C. under a pressure of 2.9 Pa with a flow rate of argon gas of 5mL/min. After the purification, 0.89 g of a yellow solid was obtained ina yield of 84%.

The yellow solid after the above purification was subjected to nuclearmagnetic resonance (NMR) spectroscopy. The measurement data are shownbelow.

¹H NMR (CDCl₃, 300 MHz): δ=7.30-7.38 (m, 3H), 7.40-7.76 (m, 23H),7.77-7.87 (m, 4H), 8.01 (d, J₁=0.90 Hz, 1H), 8.16-8.24 (m, 3H), 8.52 (d,J₁=1.2 Hz, 1H)

In addition, ¹H NMR charts are shown in FIGS. 140A and 140B. Note thatFIG. 140B is a chart where the range of from 7 ppm to 9 ppm in FIG. 140Ais enlarged. The measurement results showed that 2mDBTCzPPA-II, which isthe carbazole derivative represented by the above structural formula,was obtained.

Further, an absorption and emission spectra of 2mDBTCzPPA-II in atoluene solution of 2mDBTCzPPA-II are shown in FIG. 141A, and anabsorption and emission spectra of a thin film of 2mDBTCzPPA-II areshown in FIG. 141B. An ultraviolet-visible spectrophotometer (V-550,manufactured by JASCO Corporation) was used for the measurements of theabsorption spectra. In the case of the toluene solution, themeasurements were made with the toluene solution of 2mDBTCzPPA-II put ina quartz cell, and the absorption spectrum obtained by subtraction ofthe absorption spectra of the quartz cell and toluene from the measuredspectra is shown in the drawing. In addition, as for the absorptionspectrum of the thin film, a sample was prepared by evaporation of2mDBTCzPPA-II on a quartz substrate, and the absorption spectrumobtained by subtraction of that of quartz from the spectrum of thissample is shown in the drawing. As in the measurements of the absorptionspectra, an ultraviolet-visible spectrophotometer (V-550, manufacturedby JASCO Corporation) was used for the measurements of the emissionspectra. The emission spectrum was measured with the toluene solution of2mDBTCzPPA-II put in a quartz cell, and the emission spectrum of thethin film was measured with a sample prepared by evaporation of2mDBTCzPPA-II on a quartz substrate. Thus, it was found that theabsorption peak wavelengths of 2mDBTCzPPA-II in the toluene solution of2mDBTCzPPA-II were around 406 nm, 385 nm, 365 nm, 335 nm and 292 nm andthe emission peak wavelengths thereof were around 424 nm and 437 nm (atan excitation wavelength of 385 nm), and that the absorption peakwavelengths of the thin film of 2mDBTCzPPA-II were around 414 nm, 392nm, 370 nm, 339 nm, 295 nm, 245 nm and 208 nm and the emission peakwavelengths thereof were around 492 nm, 459 nm and 440 nm (at anexcitation wavelength of 403 nm).

Further, the ionization potential of 2mDBTCzPPA-II in a thin film statewas measured by a photoelectron spectrometer (AC-2, manufactured byRiken Keiki, Co., Ltd.) in air. The obtained value of the ionizationpotential was converted to a negative value, so that the HOMO level of2mDBTCzPPA-II was −5.74 eV. From the data of the absorption spectra ofthe thin film in FIG. 141B, the absorption edge of 2mDBTCzPPA-II, whichwas obtained from Tauc plot with an assumption of direct transition, was2.84 eV. Therefore, the optical energy gap of 2mDBTCzPPA-II in the solidstate was estimated at 2.84 eV; from the values of the HOMO levelobtained above and this energy gap, the LUMO level of 2mDBTCzPPA-II wasable to be estimated at −2.90 eV. It was thus found that 2mDBTCzPPA-IIhad a wide energy gap of 2.84 eV in the solid state.

Further, the oxidation reaction characteristics of 2mDBTCzPPA-II weremeasured. The oxidation reaction characteristics were examined by cyclicvoltammetry (CV) measurements. Note that an electrochemical analyzer(ALS model 600A or 600C, manufactured by BAS Inc.) was used for themeasurements.

For a solution for the CV measurements, dehydrated N,N-dimethylformamide(DMF, product of Sigma-Aldrich Inc., 99.8%, catalog No. 22705-6) wasused as a solvent, and tetra-n-butylammonium perchlorate (n-Bu₄NClO₄,product of Tokyo Chemical Industry Co., Ltd., catalog No. T0836), whichwas a supporting electrolyte, was dissolved in the solvent such that theconcentration thereof was 100 mmol/L. Further, the object to be measuredwas also dissolved in the solvent such that the concentration thereofwas 2 mmol/L. A platinum electrode (a PTE platinum electrode, product ofBAS Inc.) was used as a working electrode; a platinum electrode (a VC-3Pt counter electrode (5 cm), product of BAS Inc.) was used as anauxiliary electrode; and an Ag/Ag⁺ electrode (an RE5 nonaqueous solventreference electrode, product of BAS Inc.) was used as a referenceelectrode. Note that the measurements were conducted at room temperature(20° C. to 25° C.). The scan rates for the CV measurements wereuniformly set to 0.1 V/s.

In the measurements, scanning in which the potential of the workingelectrode with respect to the reference electrode was changed from 0.06V to 1.05 V and then changed from 1.05 V to 0.06 V was one cycle, and100 cycles were performed.

The measurement results revealed that 2mDBTCzPPA-II showed propertieseffective against repetition of redox reactions between an oxidizedstate and a neutral state without a large variation in oxidation peakeven after the 100 cycles in the measurements.

Further, the HOMO level of 2mDBTCzPPA-II was determined also bycalculation from the CV measurement results.

First, the potential energy of the reference electrode with respect tothe vacuum level used was found to be −4.94 eV, as determined in Example6. The oxidation peak potential E_(pa) of 2mDBTCzPPA-II was 0.91 V. Inaddition, the reduction peak potential E_(pc) thereof was 0.82 V.Therefore, a half-wave potential (an intermediate potential betweenE_(pa) and E_(pc)) can be calculated at 0.87 V. This means that2mDBTCzPPA-II is oxidized by an electric energy of 0.87 [V versusAg/Ag⁺], and this energy corresponds to the HOMO level. Here, since thepotential energy of the reference electrode, which was used in thisexample, with respect to the vacuum level is −4.94 [eV] as describedabove, the HOMO level of 2mDBTCzPPA-II was calculated as follows:−4.94−0.87=−5.81 [eV].

Example 30

In this example described is a light-emitting element in which3-(dibenzothiophen-4-yl)-9-[3-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazole(abbreviation: 2mDBTCzPPA-II, a structural formula (18)), which is oneof the carbazole derivatives represented by the general formula (G1), isused as a host material such that an emission center substance thatemits blue fluorescence is dispersed therein.

The molecular structures of organic compounds used in this example arerepresented by the structural formulae (18), (iv), and (iv) below.

In the element structure in FIG. 1A, an electron-injection layer isprovided between an electron-transport layer 114 and a second electrode104.

[Fabrication of Light-Emitting Element 18]

First, a glass substrate 101 over which indium tin oxide containingsilicon (ITSO) with a thickness of 110 nm was formed as a firstelectrode 102 was prepared. The periphery of a surface of the ITSO wascovered with a polyimide film so that an area of 2 mm×2 mm of thesurface was exposed. The electrode area was 2 mm×2 mm. As a pretreatmentfor forming the light-emitting element over the substrate, the surfaceof the substrate was washed with water and baked at 200° C. for onehour, and then a UV ozone treatment was performed for 370 seconds. Then,the substrate was transferred into a vacuum evaporation apparatus whosepressure was reduced to about 10⁻⁴ Pa, vacuum baking at 170° C. for 30minutes was performed in a heating chamber of the vacuum evaporationapparatus, and then the substrate was cooled down for about 30 minutes.

Then, the substrate was fixed on a holder provided in the vacuumevaporation apparatus such that the surface of the substrate 101provided with ITSO faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, a hole-injection layer 111 was formed by co-evaporation of9-[4-(9-phenylcarbazol-3-yl)]phenyl-10-phenylanthracene (abbreviation:PCzPA) represented by the above structural formula (v) andmolybdenum(VI) oxide such that the ratio of PCzPA:molybdenum(VI) oxidewas 2:1 (weight ratio). The thickness of was the layer was set to 50 nm.Note that the co-evaporation is an evaporation method in which aplurality of different substances is concurrently vaporized from therespective different evaporation sources.

Next, PCzPA was evaporated to a thickness of 10 nm, so that thehole-transport layer 112 was formed.

Further, the light-emitting layer 113 was formed on the hole-transportlayer 112 in such a way that3-(dibenzothiophen-4-yl)-9-[3-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazole(abbreviation: 2mDBTCzPPA-II) represented by the above structuralformula (18) andN,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenyl-pyrene-1,6-diamine(abbreviation: 1,6FLPAPm) represented by the structural formula (vi)were evaporated to form a 30-nm-thick film so that the ratio of2mDBTCzPPA-II to 1,6FLPAPrn was 1:0.03 (weight ratio).

Next, on the light-emitting layer 113,tris(8-quinolinolato)aluminum(III) (abbreviation: Alq) represented bythe above structural formula (vii) was evaporated to a thickness of 10nm, and then bathophenanthroline (abbreviation: BPhen) represented bythe above structural formula (iv) was evaporated to a thickness of 15nm, so that the electron-transport layer 114 was formed. Then, lithiumfluoride was evaporated to a thickness of 1 nm on the electron-transportlayer 114, so that the electron-injection layer was formed. Lastly, analuminum film was formed to a thickness of 200 nm as the secondelectrode 104 functioning as a cathode, so that the light-emittingelement 18 was completed. Note that in the above evaporation processes,evaporation was all performed by a resistance heating method.

[Operation Characteristics of Light-Emitting Element 18]

The light-emitting element 18 thus obtained was sealed in a glove boxunder a nitrogen atmosphere without being exposed to the air. Then, theoperation characteristics of the light-emitting element were measured.Note that the measurements were carried out at room temperature (in anatmosphere kept at 25° C.).

FIG. 142 shows luminance current density characteristics of thelight-emitting element 18, FIG. 143 shows luminance versus voltagecharacteristics thereof, FIG. 144 shows current efficiency versusluminance characteristics thereof, and FIG. 145 shows current versusvoltage characteristics thereof. In FIG. 142, the vertical axisrepresents luminance (cd/m²), and the horizontal axis represents currentdensity (mA/cm²). In FIG. 143, the vertical axis represents luminance(cd/m²), and the horizontal axis represents voltage (V). In FIG. 144,the vertical axis represents current efficiency (cd/A), and thehorizontal axis represents luminance (cd/m²). In FIG. 145, the verticalaxis represents current (mA), and the horizontal axis represents voltage(V).

FIG. 144 reveals that the light-emitting elements in each of which thecarbazole derivative represented by the general formula (G1) is used asa host material of a light-emitting layer for emitting bluefluorescence, has favorable current efficiency versus luminancecharacteristics and high emission efficiency. This is because eachcarbazole derivative represented by the general formula (G1) has a wideenergy gap, and thus even a light-emitting substance that emits bluefluorescence and has a wide energy gap can be efficiently excited. Inaddition, FIG. 143 reveals that the light-emitting elements in each ofwhich the carbazole derivative represented by the general formula (G1)is used as a host material of a light-emitting layer for emitting bluefluorescence, has favorable luminance versus voltage characteristics andcan be driven with a low voltage. This indicates that each carbazolederivative represented by the general formula (G1) has an excellentcarrier-transport property.

FIG. 146 shows an emission spectrum when a current of 1 mA was made toflow in the fabricated light-emitting element 18. The emission intensityis shown as a value relative to the greatest emission intensity assumedto be 1. FIG. 146 reveals that the light-emitting element 18 emits bluelight due to 1,6FLPAPm, which is the emission center substance.

Next, the initial luminance is set at 1000 cd/m², the element was drivenunder a condition where the current density was constant, and changes inluminance with respect to the driving time were examined. FIG. 147 showsnormalized luminance versus time characteristics. From FIG. 147, it isfound that the light-emitting element 18 shows favorable characteristicsand has high reliability.

Example 31 Synthesis Example 17

In this example is described a method of synthesizing3-(dibenzofuran-4-yl)-9-[3-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazole(abbreviation: 2mDBFCzPPA-II), which is one of the carbazole derivativesdescribed as the structural formula (19) in Embodiment 1. A structure of2mDBFCzPPA-II is illustrated in the following structural formula.

Step 1: Synthesis of 3-(Dibenzofuran-4-yl)-9H-carbazole (abbreviation:DBFCz-II)

This was synthesized as in Step 1 in Synthesis Example 2.

Step 2: Synthesis of3-(Dibenzofuran-4-yl)-9-[3-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazole(abbreviation: 2mDBFCzPPA-II)

In a 100-mL three-neck flask were put 1.0 g (2.1 mmol) of2-(3-bromophenyl)-9,10-diphenylanthracene, 0.69 g (2.1 mmol) of3-(dibenzofuran-4-yl)-9H-carbazole, and 0.59 g (6.2 mmol) of sodiumtert-butoxide. After the air in the flask was replaced with nitrogen, tothis mixture were added 20 mL of toluene and 0.2 mL oftri(tert-butyl)phosphine (a 10 wt % hexane solution). This mixture wasdegassed by being stirred while the pressure was reduced. After thedegassing, 59 mg (0.10 mmol) of bis(dibenzylideneacetone)palladium(0)was added to this mixture. This mixture was stirred at 110° C. for 5hours under a nitrogen stream. After the stirring, the obtained mixturewas suction-filtered through Celite (produced by Wako Pure ChemicalIndustries, Ltd., Catalog No. 531-16855), alumina, and Florisil(produced by Wako Pure Chemical Industries, Ltd., Catalog No.540-00135). The filtrate was concentrated to give a yellow solid. Theobtained solid was recrystallized from toluene, and the obtained crystalwas purified by high performance liquid column chromatography(abbreviation: HPLC) (chloroform as the developing solvent). Theobtained fraction was concentrated to give 0.91 g of a pale yellow solidin 60% yield. The synthesis scheme of Step 2 is illustrated in (b-17).

By a train sublimation method, the obtained pale yellow solid waspurified. The purification was conducted by heating of 0.90 g of thepale yellow solid at 335° C. under a pressure of 2.7 Pa with a flow rateof argon gas of 5 mL/min. After the purification, 0.78 g of a paleyellow solid was obtained in a yield of 87%.

The yellow solid after the above purification was subjected to nuclearmagnetic resonance (NMR) spectroscopy. The measurement data are shownbelow.

¹H NMR (CDCl₃, 300 MHz): δ=7.30-7.41 (m, 4H), 7.44-7.76 (m, 23H),7.81-7.85 (m, 2H), 7.95-8.05 (m, 4H), 8.25 (d, J₁=7.5 Hz, 1H), 8.66 (d,J₁=1.5 Hz, 1H)

In addition, ¹H NMR charts are shown in FIGS. 148A and 148B. Note thatFIG. 148B is a chart where the range of from 7 ppm to 9 ppm in FIG. 148Ais enlarged. The measurement results showed that 2mDBFCzPPA-II, which isthe carbazole derivative represented by the above structural formula,was obtained.

Further, an absorption and emission spectra of 2mDBFCzPPA-II in atoluene solution of 2mDBFCzPPA-II are shown in FIG. 149A, and anabsorption and emission spectra of a thin film of 2mDBFCzPPA-II areshown in FIG. 149B. An ultraviolet-visible spectrophotometer (V-550,manufactured by JASCO Corporation) was used for the measurements of theabsorption spectra. In the case of the toluene solution, themeasurements were made with the toluene solution of 2mDBFCzPPA-II put ina quartz cell, and the absorption spectrum obtained by subtraction ofthe absorption spectra of the quartz cell and toluene from the measuredspectra is shown in the drawing. In addition, as for the absorptionspectrum of the thin film, a sample was prepared by evaporation of2mDBFCzPPA-II on a quartz substrate, and the absorption spectrumobtained by subtraction of that of quartz from the spectrum of thissample is shown in the drawing. As in the measurements of the absorptionspectra, an ultraviolet-visible spectrophotometer (V-550, manufacturedby JASCO Corporation) was used for the measurements of the emissionspectra. The emission spectrum was measured with the toluene solution of2mDBFCzPPA-II put in a quartz cell, and the emission spectrum of thethin film was measured with a sample prepared by evaporation of2mDBFCzPPA-II on a quartz substrate. Thus, it was found that theabsorption peak wavelengths of 2mDBFCzPPA-II in the toluene solution of2mDBFCzPPA-II were around 406 nm, 385 nm, 365 nm and 291 nm and theemission peak wavelengths thereof were around 436 nm and 424 nm (at anexcitation wavelength of 386 nm), and that the absorption peakwavelengths of the thin film of 2mDBFCzPPA-II were around 414 nm, 391nm, 369 nm, 328 nm, 294 nm and 252 nm and the emission peak wavelengthsthereof were around 488 nm, 457 nm and 438 nm (at an excitationwavelength of 413 nm).

Further, the ionization potential of 2mDBFCzPPA-II in a thin film statewas measured by a photoelectron spectrometer (AC-2, manufactured byRiken Keiki, Co., Ltd.) in air. The obtained value of the ionizationpotential was converted to a negative value, so that the HOMO level of2mDBFCzPPA-II was −5.75 eV. From the data of the absorption spectra ofthe thin film in FIG. 149B, the absorption edge of 2mDBFCzPPA-II, whichwas obtained from Tauc plot with an assumption of direct transition, was2.84 eV. Therefore, the optical energy gap of 2mDBFCzPPA-II in the solidstate was estimated at 2.84 eV; from the values of the HOMO levelobtained above and this energy gap, the LUMO level of 2mDBFCzPPA-II wasable to be estimated at −2.91 eV. It was thus found that 2mDBFCzPPA-IIhad a wide energy gap of 2.84 eV in the solid state.

Further, the oxidation reaction characteristics of 2mDBFCzPPA-II weremeasured. The oxidation reaction characteristics were examined by cyclicvoltammetry (CV) measurements. Note that an electrochemical analyzer(ALS model 600A or 600C, manufactured by BAS Inc.) was used for themeasurements.

For a solution for the CV measurements, dehydrated N,N-dimethylformamide(DMF, product of Sigma-Aldrich Inc., 99.8%, catalog No. 22705-6) wasused as a solvent, and tetra-n-butylammonium perchlorate (n-Bu₄NClO₄,product of Tokyo Chemical Industry Co., Ltd., catalog No. T0836), whichwas a supporting electrolyte, was dissolved in the solvent such that theconcentration thereof was 100 mmol/L. Further, the object to be measuredwas also dissolved in the solvent such that the concentration thereofwas 2 mmol/L. A platinum electrode (a PTE platinum electrode, product ofBAS Inc.) was used as a working electrode; a platinum electrode (a VC-3Pt counter electrode (5 cm), product of BAS Inc.) was used as anauxiliary electrode; and an Ag/Ag⁺ electrode (an RE5 nonaqueous solventreference electrode, product of BAS Inc.) was used as a referenceelectrode. Note that the measurements were conducted at room temperature(20° C. to 25° C.). The scan rates for the CV measurements wereuniformly set to 0.1 V/s.

In the measurements, scanning in which the potential of the workingelectrode with respect to the reference electrode was changed from −0.41V to 1.05 V and then changed from 1.05 V to −1.41 V was one cycle, and100 cycles were performed.

The measurement results revealed that 2mDBFCzPPA-II showed propertieseffective against repetition of redox reactions between an oxidizedstate and a neutral state without a large variation in oxidation peakeven after the 400 cycles in the measurements.

Further, the HOMO level of 2mDBFCzPPA-II was determined also bycalculation from the CV measurement results.

First, the potential energy of the reference electrode with respect tothe vacuum level used was found to be −4.94 eV, as determined in Example6. The oxidation peak potential E_(pa) of 2mDBFCzPPA-II was 0.93 V. Inaddition, the reduction peak potential E_(pc) thereof was 0.82 V.Therefore, a half-wave potential (an intermediate potential betweenE_(pa) and E_(pc)) can be calculated at 0.88 V. This means that2mDBFCzPPA-II is oxidized by an electric energy of 0.88 [V versusAg/Ag⁺], and this energy corresponds to the HOMO level. Here, since thepotential energy of the reference electrode, which was used in thisexample, with respect to the vacuum level is −4.94 [eV] as describedabove, the HOMO level of 2mDBFCzPPA-II was calculated as follows:−4.94−0.88=−5.82 [eV].

Example 32

In this example described is a light-emitting element in which3-(dibenzofuran-4-yl)-9-[3-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazole(abbreviation: 2mDBFCzPPA-II, a structural formula (19)), which is oneof the carbazole derivatives represented by the general formula (G1), isused as a host material such that an emission center substance thatemits blue fluorescence is dispersed therein.

The molecular structures of organic compounds used in this example arerepresented by the structural formulae (19), (iv), and (iv) below.

In the element structure in FIG. 1A, an electron-injection layer isprovided between an electron-transport layer 114 and a second electrode104.

[Fabrication of Light-Emitting Element 19]

First, a glass substrate 101 over which indium tin oxide containingsilicon (ITSO) with a thickness of 110 nm was formed as a firstelectrode 102 was prepared. The periphery of a surface of the ITSO wascovered with a polyimide film so that an area of 2 mm×2 mm of thesurface was exposed. The electrode area was 2 mm×2 mm. As a pretreatmentfor forming the light-emitting element over the substrate, the surfaceof the substrate was washed with water and baked at 200° C. for onehour, and then a UV ozone treatment was performed for 370 seconds. Then,the substrate was transferred into a vacuum evaporation apparatus whosepressure was reduced to about 10⁻⁴ Pa, vacuum baking at 170° C. for 30minutes was performed in a heating chamber of the vacuum evaporationapparatus, and then the substrate was cooled down for about 30 minutes.

Then, the substrate was fixed on a holder provided in the vacuumevaporation apparatus such that the surface of the substrate 101provided with ITSO faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, a hole-injection layer 111 was formed by co-evaporation of9-[4-(9-phenylcarbazol-3-yl)]phenyl-10-phenylanthracene (abbreviation:PCzPA) represented by the above structural formula (v) andmolybdenum(VI) oxide such that the ratio of PCzPA:molybdenum(VI) oxidewas 2:1 (weight ratio). The thickness of was the layer was set to 50 nm.Note that the co-evaporation is an evaporation method in which aplurality of different substances is concurrently vaporized from therespective different evaporation sources.

Next, PCzPA was evaporated to a thickness of 10 nm, so that thehole-transport layer 112 was formed.

Further, the light-emitting layer 113 was formed on the hole-transportlayer 112 in such a way that3-(dibenzofuran-4-yl)-9-[3-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazole(abbreviation: 2mDBFCzPPA-II) represented by the above structuralformula (19) andN,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenyl-pyrene-1,6-diamine(abbreviation: 1,6FLPAPm) represented by the structural formula (vi)were evaporated to form a 30-nm-thick film so that the ratio of2mDBFCzPPA-II to 1,6FLPAPm was 1:0.05 (weight ratio).

Next, on the light-emitting layer 113,tris(8-quinolinolato)aluminum(III) (abbreviation: Alq) represented bythe above structural formula (vii) was evaporated to a thickness of 10nm, and then bathophenanthroline (abbreviation: BPhen) represented bythe above structural formula (iv) was evaporated to a thickness of 15nm, so that the electron-transport layer 114 was formed. Then, lithiumfluoride was evaporated to a thickness of 1 nm on the electron-transportlayer 114, so that the electron-injection layer was formed. Lastly, analuminum film was foamed to a thickness of 200 nm as the secondelectrode 104 functioning as a cathode, so that the light-emittingelement 19 was completed. Note that in the above evaporation processes,evaporation was all performed by a resistance heating method.

[Operation Characteristics of Light-Emitting Element 19]

The light-emitting element 19 thus obtained was sealed in a glove boxunder a nitrogen atmosphere without being exposed to the air. Then, theoperation characteristics of the light-emitting element were measured.Note that the measurements were carried out at room temperature (in anatmosphere kept at 25° C.).

FIG. 150 shows luminance current density characteristics of thelight-emitting element 19, FIG. 151 shows luminance versus voltagecharacteristics thereof, FIG. 152 shows current efficiency versusluminance characteristics thereof, and FIG. 153 shows current versusvoltage characteristics thereof. In FIG. 150, the vertical axisrepresents luminance (cd/m²), and the horizontal axis represents currentdensity (mA/cm²). In FIG. 151, the vertical axis represents luminance(cd/m²), and the horizontal axis represents voltage (V). In FIG. 152,the vertical axis represents current efficiency (cd/A), and thehorizontal axis represents luminance (cd/m²). In FIG. 153, the verticalaxis represents current (mA), and the horizontal axis represents voltage(V).

FIG. 152 reveals that the light-emitting elements in each of which thecarbazole derivative represented by the general formula (G1) is used asa host material of a light-emitting layer for emitting bluefluorescence, has favorable current efficiency versus luminancecharacteristics and high emission efficiency. This is because eachcarbazole derivative represented by the general formula (G1) has a wideenergy gap, and thus even a light-emitting substance that emits bluefluorescence and has a wide energy gap can be efficiently excited. Inaddition, FIG. 151 reveals that the light-emitting elements in each ofwhich the carbazole derivative represented by the general formula (G1)is used as a host material of a light-emitting layer for emitting bluefluorescence, has favorable luminance versus voltage characteristics andcan be driven with a low voltage. This indicates that each carbazolederivative represented by the general formula (G1) has an excellentcarrier-transport property.

FIG. 154 shows an emission spectrum when a current of 1 mA was made toflow in the fabricated light-emitting element 19. The emission intensityis shown as a value relative to the greatest emission intensity assumedto be 1. FIG. 154 reveals that the light-emitting element 19 emits bluelight due to 1,6FLPAPrn, which is the emission center substance.

Next, the initial luminance is set at 1000 cd/m², the element was drivenunder a condition where the current density was constant, and changes inluminance with respect to the driving time were examined. FIG. 155 showsnormalized luminance versus time characteristics. From FIG. 155, it isfound that the light-emitting element 19 shows favorable characteristicsand has high reliability

Reference Example 1

A method of synthesizing4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP)(structural formula (i)) used in the above Examples will be specificallydescribed. A structure of BPAFLP is illustrated below.

Step 1: Method of Synthesizing 9-(4-Bromophenyl)-9-phenylfluorene

In a 100-mL three-neck flask, 1.2 g (50 mmol) of magnesium was heatedand stirred for 30 minutes under reduced pressure to be activated. Theactivated magnesium was cooled to room temperature, and the flask wasmade to contain a nitrogen atmosphere. Then, several drops ofdibromoethane were added, so that foam formation and heat generationwere confirmed. After 12 g (50 mmol) of 2-bromobiphenyl dissolved in 10mL of diethyl ether was slowly added dropwise to this mixture, themixture was heated and stirred under reflux for 2.5 hours, so that aGrignard reagent was prepared.

Into a 500-mL three-neck flask were placed 10 g (40 mmol) of4-bromobenzophenone and 100 mL of diethyl ether. After the Grignardreagent which was synthesized in advance was slowly added dropwise tothis mixture, the mixture was heated and stirred under reflux for 9hours.

After reaction, this mixture solution was filtered to give a residue.The obtained residue was dissolved in 150 mL of glacial acetic acid, and1M hydrochloric acid was added to the mixture until it was made acid,which was then stirred for 2 hours. The organic layer of this mixturewas washed with water, and magnesium sulfate was added thereto to adsorbmoisture. This suspension was filtered, and the obtained filtrate wasconcentrated to give an oily substance.

Into a 500-mL recovery flask were placed this oily substance, 50 mL ofglacial acetic acid, and 1.0 mL of hydrochloric acid. The mixture wasstirred and heated at 130° C. for 1.5 hours under a nitrogen atmosphereto be reacted.

After the reaction, this reaction mixture solution was filtered to givea residue. The obtained residue was washed with water, an aqueous sodiumhydroxide solution, water, and methanol in this order. Then, the mixturewas dried, so that the substance which was the object of the synthesiswas obtained as 11 g of a white powder in 69% yield. A reaction schemeof the above synthesis method is illustrated in the following (J-3).

Step 2: Method of Synthesizing4-Phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP)

Into a 100-mL three-neck flask were placed 3.2 g (8.0 mmol) of9-(4-bromophenyl)-9-phenylfluorene, 2.0 g (8.0 mmol) of4-phenyl-diphenylamine, 1.0 g (10 mmol) of sodium tert-butoxide, and 23mg (0.04 mmol) of bis(dibenzylideneacetone)palladium(0), and the air inthe flask was replaced with nitrogen. Then, 20 mL of dehydrated xylenewas added to this mixture. After the mixture was degassed by beingstirred under reduced pressure, 0.2 mL (0.1 mmol) oftri(tert-butyl)phosphine (a 10 wt % hexane solution) was added to themixture. This mixture was stirred and heated at 110° C. for 2 hoursunder a nitrogen atmosphere to be reacted.

After the reaction, 200 mL of toluene was added to this reactionmixture, and this suspension was filtered through Florisil (produced byWako Pure Chemical Industries, Ltd., Catalog No. 540-00135) and Celite(produced by Wako Pure Chemical Industries, Ltd., Catalog No.531-16855). The obtained filtrate was concentrated, and the resultingsubstance was purified by silica gel column chromatography (a developingsolvent in which the toluene/hexane ratio was 1:4). The obtainedfraction was concentrated, and acetone and methanol were added to themixture. The mixture was irradiated with ultrasonic waves and thenrecrystallized, so that the substance which was the object of thesynthesis was obtained as 4.1 g of a white powder in 92% yield. Areaction scheme of the above synthesis method is illustrated in thefollowing (J-4).

The Rf values of the substance that was the object of the synthesis,9-(4-bromophenyl)-9-phenylfluorene, and 4-phenyl-diphenylamine wererespectively 0.41, 0.51, and 0.27, which were found by silica gel thinlayer chromatography (TLC) (a developing solvent in which the ethylacetate/hexane ratio was 1:10).

The compound obtained in the above Step 2 was subjected to nuclearmagnetic resonance (NMR) spectroscopy. The measurement data are shownbelow. The measurement results indicate that the obtained compound wasBPAFLP, which is a fluorene derivative.

¹H NMR (CDCl₃, 300 MHz): δ (ppm)=6.63-7.02 (m, 3H), 7.06-7.11 (m, 6H),7.19-7.45 (m, 18H), 7.53-7.55 (m, 2H), 7.75 (d, J=6.9, 2H).

Reference Example 2

A method of synthesizingN,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenyl-pyrene-1,6-diamine(abbreviation: 1,6FLPAPrn) (structural formula (vi)) used in the aboveExamples will be specifically described. A structure of 1,6FLPAPm isillustrated below.

Step 1: Method of Synthesizing 9-(4-Bromophenyl)-9-phenylfluorene

In a 100-mL three-neck flask, 1.2 g (50 mmol) of magnesium was heatedand stirred for 30 minutes under reduced pressure to be activated. Theactivated magnesium was cooled to room temperature, and the flask wasmade to contain a nitrogen atmosphere. Then, several drops ofdibromoethane were added, so that foam formation and heat generationwere confirmed. After 12 g (50 mmol) of 2-bromobiphenyl dissolved in 10mL of diethyl ether was slowly added dropwise to this mixture, themixture was heated and stirred under reflux for 2.5 hours, so that aGrignard reagent was prepared.

Into a 500-mL three-neck flask were placed 10 g (40 mmol) of4-bromobenzophenone and 100 mL of diethyl ether. After the Grignardreagent which was synthesized in advance was slowly added dropwise tothis mixture, the mixture was heated and stirred under reflux for 9hours.

After reaction, this mixture solution was filtered to give a residue.The obtained residue was dissolved in 150 mL of ethyl acetate, and 1Mhydrochloric acid was added to the mixture, which was then stirred for 2hours. The organic layer of this liquid was washed with water, andmagnesium sulfate was added thereto to remove moisture. This suspensionwas filtered, and the obtained filtrate was concentrated to give an oilysubstance.

Into a 500-mL recovery flask were placed this oily substance, 50 mL ofglacial acetic acid, and 1.0 mL of hydrochloric acid. The mixture wasstirred and heated at 130° C. for 1.5 hours under a nitrogen atmosphereto be reacted:

After the reaction, this reaction mixture was filtered to give aresidue. The obtained residue was washed with water, an aqueous sodiumhydroxide solution, water, and methanol in this order. Then, the mixturewas dried, so that the substance which was the object of the synthesiswas obtained as 11 g of a white powder in 69% yield. The synthesisscheme of the above Step 1 is illustrated in (E1-1) below.

Step 2: Method of Synthesizing 4-(9-Phenyl-9H-fluoren-9-yl)diphenylamine(abbreviation: FLPA)

In a 200 mL three-neck flask were put 5.8 g (14.6 mmol) of9-(4-bromophenyl)-9-phenylfluorene, 1.7 mL (18.6 mmol) of aniline, and4.2 g (44.0 mmol) of sodium tert-butoxide. The air in the flask wasreplaced with nitrogen. To this mixture were added 147.0 mL of tolueneand 0.4 mL of a 10% hexane solution of tri(tert-butyl)phosphine. Thetemperature of this mixture was set to 60° C., and 66.1 mg (0.1 mmol) ofbis(dibenzylideneacetone)palladium(0) was added to the mixture, followedby stirring for 3.5 hours. After the stirring, the mixture wassuction-filtered through Florisil (produced by Wako Pure ChemicalIndustries, Ltd., Catalog No. 540-00135), Celite (produced by Wako PureChemical Industries, Ltd., Catalog No. 531-16855), and alumina. Theobtained filtrate was concentrated. The obtained filtrate wasconcentrated to give a solid, which was then purified by silica gelcolumn chromatography (the developing solvent has a 2:1 ratio of hexaneto toluene). The obtained fraction was concentrated to give 6.0 g of awhite solid in 99% yield, which was the object of the synthesis. Thesynthesis scheme of Step 2 is shown in (E1-2) below.

Step 3: Method of SynthesizingN,N′-Bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenyl-pyrene-1,6-diamine(abbreviation: 1,6FLPAPm)

In a 50 mL three-neck flask were put 0.4 g (1.2 mmol) of1,6-dibromopyrene, 1.0 g (2.4 mmol) of4-(9-phenyl-9H-fluoren-9-yl)diphenylamine (abbreviation: FLPA), whichwas obtained in Step 2 in Reference Example 2, and 0.3 g (3.6 mmol) ofsodium tert-butoxide. The air in the flask was replaced with nitrogen.To this mixture were added 11.5 mL of toluene and 0.20 mL of a 10%hexane solution of tri(tert-butyl)phosphine. The temperature of thismixture was set to 70° C., and 31.1 mg (0.05 mmol) ofbis(dibenzylideneacetone)palladium(0) was added to the mixture, followedby stirring for 4.0 hours. After the stirring, the mixture wassuction-filtered through Florisil, Celite, and alumina. The obtainedfiltrate was concentrated. The obtained filtrate was concentrated togive a solid, which was then purified by silica gel columnchromatography (the developing solvent was chloroform). The obtainedfraction was concentrated to give a yellow solid. The obtained solid waswashed with a mixed solvent of toluene and hexane, and then the mixturewas suction-filtered to give a yellow solid. The obtained yellow solidwas washed with a mixed solvent of chloroform and hexane, so that 0.8 gof a pale yellow powdered solid was obtained in 68% yield.

By a train sublimation method, 0.8 g of the obtained pale yellow solidwas purified. Under a pressure of 2.7 Pa with a flow rate of argon at5.0 mL/min, the sublimation purification was carried out at 360° C.After the purification, 0.4 g of the object of the synthesis wasobtained in a yield of 56%. The synthesis scheme of the above Step 3 isshown in the following (E2-A).

A nuclear magnetic resonance (NMR) method and a mass spectrometryidentified the obtained compound asN,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenyl-pyrene-1,6-diamine(abbreviation: 1,6FLPAPm). The ¹H NMR data is given as follows.

¹H NMR data of the obtained compound are: ¹H NMR (CDCl₃, 300 MHz):δ=6.88-6.91 (m, 6H), 7.00-7.03 (m, 8H), 7.13-7.40 (m, 26H), 7.73-7.80(m, 6H), 7.87 (d, J=9.0 Hz, 2H), 8.06-8.09 (m, 4H).

Reference Example 3

In this reference example, a method of synthesizingN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn) used in the above Examples will bedescribed.

Step 1: Method of Synthesizing3-Methylphenyl-3-(9-phenyl-9H-fluoren-9-yl)phenylamine (abbreviation:mMemFLPA)

In a 200 mL three-neck flask were put 3.2 g (8.1 mmol) of9-(3-bromophenyl)-9-phenylfluorene and 2.3 g (24.1 mmol) of sodiumtert-butoxide. The air in the flask was replaced with nitrogen. To thismixture were added 40.0 mL of toluene, 0.9 mL (8.3 mmol) of m-toluidine,and 0.2 mL of a 10% hexane solution of tri(tert-butyl)phosphine. Thetemperature of this mixture was set to 60° C., and 44.5 mg (0.1 mmol) ofbis(dibenzylideneacetone)palladium(0) was added to the mixture. Thetemperature of the mixture was raised to 80° C., followed by stirringfor 2.0 hours. After the stirring, the mixture was suction-filteredthrough Florisil (produced by Wako Pure Chemical Industries, Ltd.,Catalog No. 540-00135), Celite (produced by Wako Pure ChemicalIndustries, Ltd., Catalog No. 531-16855), and alumina to give afiltrate. The filtrate was concentrated to give a solid, which was thenpurified by silica gel column chromatography (the developing solvent hasa 1:1 ratio of hexane to toluene). Recrystallization from a mixedsolvent of toluene and hexane was performed. Accordingly, 2.8 g of awhite solid was obtained in 82% yield, which was the object of thesynthesis. The synthesis scheme of this Step 1 is illustrated below.

Step 2: Method of SynthesizingN,N′-Bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine (abbreviation: 1,6mMemFLPAPrn.)

In a 100 mL three-neck flask were put 0.6 g (1.7 mmol) of1,6-dibromopyrene, 1.4 g (3.4 mmol) of3-methylphenyl-3-(9-phenyl-9H-fluoren-9-yl)phenylamine, and 0.5 g (5.1mmol) of sodium tert-butoxide. The air in the flask was replaced withnitrogen. To this mixture were added 21.0 mL of toluene and 0.2 mL of a10% hexane solution of tri(tert-butyl)phosphine. The temperature of thismixture was set to 60° C., and 34.9 mg (0.1 mmol) ofbis(dibenzylideneacetone)palladium(0) was added to the mixture. Thetemperature of this mixture was raised to 80° C., followed by stirringfor 3.0 hours. After the stirring, 400 mL of toluene was added to themixture, and the mixture was heated. While the mixture was kept hot, itwas suction-filtered through Florisil (produced by Wako Pure ChemicalIndustries, Ltd., Catalog No. 540-00135), Celite (produced by Wako PureChemical Industries, Ltd., Catalog No. 531-16855), and alumina to give afiltrate. The filtrate was concentrated to give a solid, which was thenpurified by silica gel column chromatography (the developing solvent hasa 3:2 ratio of hexane to toluene) to give a yellow solid.Recrystallization of the obtained yellow solid from a mixed solvent oftoluene and hexane gave 1.2 g of a yellow solid in 67% yield, which wasthe object of the synthesis.

By a train sublimation method, 1.0 g of the obtained yellow solid waspurified. In the purification, the yellow solid was heated at 317° C.under a pressure of 2.2 Pa with a flow rate of argon gas of 5.0 mL/min.After the purification, 1.0 g of a yellow solid was obtained in a yieldof 93%, which was the object of the synthesis. The synthesis scheme ofStep 2 is shown below.

A nuclear magnetic resonance (NMR) method identified this compound asN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn), which was the object of the synthesis.

¹H NMR data of the obtained compound are: ¹H NMR (CDCl₃, 300 MHz):δ=2.21 (s, 6H), 6.67 (d, J=7.2 Hz, 2H), 6.74 (d, J=7.2 Hz, 2H),7.17-7.23 (m, 34H), 7.62 (d, J=7.8 Hz, 4H), 7.74 (d, J=7.8 Hz, 2H), 7.86(d, J=9.0 Hz, 2H), 8.04 (d, J=8.7 Hz, 4H).

Reference Example 4

A synthesis example oftris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III)(abbreviation: [Ir(Mptz1-mp)₃]), which was a material used in theExample, will be described.

Step 1: Synthesis of N-(1-Ethoxyethylidene)benzamide

First, 15.5 g of ethyl acetimidate hydrochloride, 150 mL of toluene, and31.9 g of triethylamine (Et₃N) were put into a 500-mL three-neck flaskand stirred at room temperature for 10 minutes. With a 50-mL droppingfunnel, a mixed solution of 17.7 g of benzoyl chloride and 30 mL oftoluene were added dropwise to this mixture, and the mixture was stirredat room temperature for 24 hours. After a predetermined time elapsed,the reaction mixture was suction-filtered, and the solid was washed withtoluene. The obtained filtrate was concentrated to giveN-(1-ethoxyethylidene)benzamide (a red oily substance, 82% yield). Ascheme of the synthesis of Step 1 is shown below.

Step 2: Synthesis of3-Methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazole (abbreviation:HMptz1-mp)

Next, into a 300-mL recovery flask were put 8.68 g of o-tolyl hydrazinehydrochloride, 100 mL of carbon tetrachloride, and 35 mL oftriethylamine (Et₃N), and the mixture was stirred at room temperaturefor 1 hour. After a predetermined time elapsed, 8.72 g ofN-(1-ethoxyethylidene)benzamide obtained in the above Step 1 was addedto this mixture, and the mixture was stirred at room temperature for 24hours. After a predetermined time elapsed, water was added to thereaction mixture, and the aqueous layer was subjected to extraction withchloroform. The organic layer of the resulting mixture was washed withsaturated brine, and dried with anhydrous magnesium sulfate addedthereto. The obtained mixture was gravity-filtered, and the filtrate wasconcentrated to give an oily substance. The obtained oily substance waspurified by silica gel column chromatography. Dichloromethane was usedas a developing solvent. The obtained fraction was concentrated to give3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazole (abbreviation:HMptz1-mp) (an orange oily substance, 84% yield). A synthesis scheme ofStep 2 is shown below.

Step 3: Synthesis ofTris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III)(abbreviation: [Ir(Mptz1-mp)₃])

Next, 2.71 g of the ligand HMptz1-mp obtained in the above Step 2 and1.06 g of tris(acetylacetonato)iridium(III) were put into a reactioncontainer provided with a three-way cock. The air in this flask wasreplaced with argon, and heated at 250° C. for 48 hours to be reacted.This reaction mixture was dissolved in dichloromethane and purified bysilica gel column chromatography. As the developing solvent,dichloromethane was first used, and a mixed solvent of dichloromethaneand ethyl acetate in a ratio of 10:1 (v/v) was then used. The obtainedfraction was concentrated to give a solid. This solid was washed withethyl acetate, and recrystallized from a mixed solvent ofdichloromethane and ethyl acetate to give the organometallic complexIr(Mptz1-mp)₃ (a yellow powder, 35% yield). A scheme of the synthesis ofStep 3 is shown below.

Analysis results by nuclear magnetic resonance spectrometry (¹H-NMR) ofthe yellow powder obtained in the above Step 3 are shown below. Thus,[Ir(Mptz1-mp)₃] was found to be obtained.

¹H NMR data of the obtained substance are as follows: ¹H NMR (CDCl₃):1.94-2.21 (m, 18H), 6.47-6.76 (m, 12H), 7.29-7.52 (m, 12H).

Reference Example 5

A synthesis example of2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole(abbreviation: mDBTBIm-II), which was a material used in Example, willbe described.

Synthesis of2-[3-(Dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole(abbreviation: mDBTBIm-II)

Into a 50-mL three-neck flask were put 1.2 g (3.3 mmol) of2-(3-bromophenyl)-1-phenyl-1H-benzimidazole, 0.8 g (3.3 mmol) ofdibenzothiophen-4-boronic acid, and 50 mg (0.2 mmol) oftri(ortho-tolyl)phosphine. The air in the flask was replaced withnitrogen. To this mixture were added 3.3 mL of a 2.0 mmol/L aqueoussolution of potassium carbonate, 12 mL of toluene, and 4 mL of ethanol.Under reduced pressure, this mixture was stirred to be degassed. Then,7.4 mg (33 μmol) of palladium(II) acetate was added to this mixture, andthe mixture was stirred at 80° C. for 6 hours under a nitrogen stream.After a predetermined time, the aqueous layer of the obtained mixturewas subjected to extraction with toluene. The solution of the obtainedextract combined with the organic layer was washed with saturated brine,and then the organic layer was dried over magnesium sulfate. Thismixture was separated by gravity filtration, and the filtrate wasconcentrated to give an oily substance. This oily substance was purifiedby silica gel column chromatography. The silica gel columnchromatography was carried out using toluene as a developing solvent.The obtained fraction was concentrated to give an oily substance. Thisoily substance was purified by high performance liquid chromatography.The high performance liquid chromatography was performed usingchloroform as a developing solvent. The obtained fraction wasconcentrated to give an oily substance. This oily substance wasrecrystallized from a mixed solvent of toluene and hexane, so that thesubstance which was the object of the synthesis was obtained as 0.8 g ofa pale yellow powder in 51% yield. The synthesis scheme is illustratedin the following formula.

By a train sublimation method, 0.8 g of the obtained pale yellow powderwas purified. In the purification, the pale yellow powder was heated at215° C. under a pressure of 3.0 Pa with a flow rate of argon gas of 5mL/min After the purification, 0.6 g of a white powder of the substancewhich was the object of the synthesis was obtained in a yield of 82%.

This compound was identified as2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole(abbreviation: mDBTBIm-II), which was the object of the synthesis, bynuclear magnetic resonance (NMR) spectroscopy.

¹H NMR data of the obtained compound are as follows: ¹H NMR (CDCl₃, 300MHz): δ (ppm)=7.23-7.60 (m, 13H), 7.71-7.82 (m, 3H), 7.90-7.92 (m, 2H),8.10-8.17 (m, 2H).

REFERENCE NUMERALS

-   101: substrate, 102: first electrode, 103: EL layer, 104: second    electrode, 111: hole-injection layer, 112: hole-transport layer,    113: light-emitting layer, 114: electron-transport layer, 501: first    electrode, 502: second electrode, 511: first light-emitting unit,    512: second light-emitting unit, 513: charge generation layer, 601:    driver circuit portion: (source side driver circuit), 602: pixel    portion, 603: driver circuit portion: (gate side driver circuit),    604: sealing substrate, 605: sealing material, 607: space, 608:    wiring, 609: FPC (flexible printed circuit), 610: element substrate,    611: switching TFT, 612: current controlling TFT, 613: first    electrode, 614: insulator, 616: layer containing organic compound,    617: second electrode, 618: light-emitting element, 623: n-channel    TFT, 624: p-channel TFT, 901: housing, 902: liquid crystal layer,    903: backlight unit, 904: housing, 905: driver IC, 906: terminal,    951: substrate, 952: electrode, 953: insulating layer, 954:    partition layer, 955: a layer containing an organic compound, 956:    electrode, 2001: housing, 2002: light source, 3001: lighting device,    9101: housing, 9102: support, 9103: display portion, 9104: speaker    portion, 9105: video input terminal, 9201: main body, 9202: housing,    9203: display portion, 9204: keyboard, 9205: external connection    port, 9206: pointing device, 9401: main body, 9402: housing, 9403:    display portion, 9404: audio input portion, 9405: audio output    portion, 9406: operation key, 9407: external connection port, 9408:    antenna, 9501: main body, 9502: display portion, 9503: housing,    9504: external connection port, 9505: remote control receiving    portion, 9506: image receiving portion, 9507: battery, 9508: audio    input portion, 9509: operation key, 9510: eye piece portion.

This application is based on Japanese Patent Application serial No.2010-203396 filed with the Japan Patent Office on Sep. 10, 2010, theentire contents of which are hereby incorporated by reference.

The invention claimed is:
 1. A light-emitting element comprising a layercontaining an organic compound between a pair of electrodes, wherein theorganic compound contains a carbazole group, wherein a 4-position of adibenzothiophene skeleton or a 4-position of a dibenzofuran skeleton isbonded to a 2- or 3-position of the carbazole group, wherein an arylgroup is bonded to a 9-position of the carbazole group, and wherein thearyl group has 6 to 70 carbon atoms and comprises a substituent selectedfrom a benzimidazolyl group, a benzoxazolyl group, and an oxadiazolylgroup.
 2. The light-emitting element according to claim 1, wherein a4-position of a dibenzothiophene skeleton or a 4-position of adibenzofuran skeleton is further bonded to a 6- or 7-position ofcarbazole the carbazole group.
 3. A light-emitting element comprising alayer containing an organic compound between a pair of electrodes,wherein the organic compound contains a carbazole group, wherein a4-position of a dibenzothiophene skeleton or a 4-position of adibenzofuran skeleton is bonded to 2- and 7-positions of the carbazolegroup or 3- and 6-positions of the carbazole group, wherein an arylgroup is bonded to a 9-position of the carbazole group, and wherein thearyl group has 6 to 70 carbon atoms and comprises a substituent selectedfrom a benzimidazolyl group, a benzoxazolyl group, and an oxadiazolylgroup.
 4. A light-emitting element comprising a layer containing anorganic compound between a pair of electrodes, wherein the organiccompound is represented by a formula (G1):

wherein: Ar represents an aryl group having 6 to 70 carbon atoms andcomprises a substituent selected from a benzimidazolyl group, abenzoxazolyl group, and an oxadiazolyl group; R⁰ represents asubstituent represented by a formula (g1):

R⁸ represents any one of hydrogen, an alkyl group having 1 to 6 carbonatoms, an aryl group having 6 to 15 carbon atoms, and a groupsubstituent represented by a formula (g2):

a substitution site of R⁰ is a carbon atom represented by either a or β,and a substitution site of R⁸ is a carbon atom represented by either γor δ, and wherein: X¹ and X² individually represent oxygen or sulfur;and R¹ to R⁷ and R⁹ to R¹⁵ individually represent any one of hydrogen,an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to15 carbon atoms.
 5. The light-emitting element according to claim 4,wherein R⁸ is bonded to the carbon atom represented by γ when R⁸ is thesubstituent represented by the formula (g2) and R⁰ is bonded to thecarbon atom represented by α, and wherein R⁸ is bonded to the carbonatom represented by δ when R⁸ is the substituent represented by theformula (g2) and R⁰ is bonded to the carbon atom represented by β. 6.The light-emitting element according to claim 4, wherein: R⁰ representsa substituent represented by a formula (g3):

R⁸ represents any one of hydrogen, an aryl group having 6 to 15 carbonatoms, an alkyl group having 1 to 6 carbon atoms, and a substituentrepresented by a formula (g4):


7. The light-emitting element according to claim 6, wherein R⁸ is bondedto the carbon atom represented by γ when R⁸ is the substituentrepresented by the formula (g4) and R⁰ is bonded to the carbon atomrepresented by α, and wherein R⁸ is bonded to the carbon atomrepresented by δ when R⁸ is the substituent represented by the formula(g4) and R⁰ is bonded to the carbon atom represented by β.
 8. Thelight-emitting element according to claim 6, wherein: R⁸ represents anyof hydrogen and the substituent represented by the formula (g4).
 9. Thelight-emitting element according to claim 4, wherein: R⁰ represents asubstituent represented by a formula (g5):

R⁸ represents any of hydrogen and a substituent represented by a formula(g6):


10. The light-emitting element according to claim 9, wherein R⁸ isbonded to the carbon atom represented by γ when R⁸ is the substituentrepresented by the formula (g6) and R⁰ is bonded to the carbon atomrepresented by α, and wherein R⁸ is bonded to the carbon atomrepresented by δ when R⁸ is the substituent represented by the formula(g6) and R⁰ is bonded to the carbon atom represented by β.
 11. Thelight-emitting element according to claim 4, wherein the organiccompound is represented by a formula (G2):

wherein X represents oxygen or sulfur.
 12. The light-emitting elementaccording to claim 4, wherein the organic compound is represented by aformula (G3):


13. The light-emitting element according to claim 4, wherein the organiccompound is represented by a formula (G4):


14. The light-emitting element according to claim 4, wherein X¹ and X²each are sulfur.